WO1989006202A1

WO1989006202A1 - Process and device for operating a windscreen wiper

Info

Publication number: WO1989006202A1
Application number: PCT/DE1988/000790
Authority: WO
Inventors: Hermann Winner
Original assignee: Robert Bosch Gmbh
Priority date: 1988-01-08
Filing date: 1988-12-31
Publication date: 1989-07-13
Also published as: DE3800327A1

Abstract

In a process for operating a windscreen wiper, a beam of radiation (11) emitted by a radiation source (10) is input at a definite angle (16) into a windscreen (13) the outer surface (14) of which is to be cleaned by a windscreen wiper. The angle (16) is closen so that the beam (11) is totally reflected at the outer (14) and inner (19) surfaces of the windscreen, from which it emerges at a particular position and is directed to a radiation receiver (21). When the outer surface (14) of the windscreen is wetted with drops of water (22-25), a loss radiation (28, 29) is output. This results in a reduction of the signal (43) emitted by the radiation receiver (21). If the signal (43) falls below a threshold by a predetermined amount, a cleaning process of the windscreen wiper is initiated. The threshold is established in function of the peak value of the signal (43). The measured peak value is stored, the input time being appreciably shorter than the duration of storage.

Description

Method for operating a windshield wiper and device for carrying out the method

State of the art

The invention is based on a method for operating a windshield wiper according to the preamble of claim 1 and a device for carrying out the method according to the preamble of claim 8.

A window contamination detector is known from DE-AS 23 54 100, which is based on an optical measuring method. The light emitted by a light source through a pane hits a pane surface to be tested. The light thrown back through the window on the soiled surface of the window is received by a light measuring device to which a signal transmitter is connected which, for example, triggers a wiping process of a window wiper. Only those light parts emitted by the light source and thrown back on the soiled pane surface are detected by the light measuring device, which emanate from the soiled pane surface at the angle of total reflection, being passed through a prismatic device when leaving the pane. The light measuring device measures a certain value with undisturbed total reflection, which represents a zero point value. If the intensity of the total reflected light changes due to water drops or solid dirt particles, the light measuring device detects new measured values and forwards them to the signal transmitter, which is set to a defined limit value. If this limit is exceeded, a signal is issued that switches on the wiper.

A moisture detector for controlling windshield wipers is known from the conference volume "Transducers '87", pages 73-75, in which the change in intensity of a light beam guided in a windshield is also used to detect contamination of the windshield surface. A light-emitting diode is used as the light source and is operated in a pulsed manner. The signal picked up by a radiation receiver is fed to a bandpass filter and then to a demodulator. The output signal from the demodulator is sent to a comparator with a variable threshold. The comparator threshold is determined experimentally and then set. The signal for switching on the windshield wiper is available at the output of the comparator.

Advantages of the invention

The method according to the invention has the advantage that the threshold is tracked as a function of the peak value of the signal emitted by the radiation receiver. This measure makes the automatic operation of a windshield wiper independent of the sample scatter and the assembly uncertainty of all components. Furthermore, the long-term drift and the temperature drift of all components are eliminated. In addition, the condition of the surface of the pane is taken into account, which is constantly changing, for example due to scratches. The method can be implemented technically with little effort and increases the operational reliability in the automatic operation of the windshield wiper in a particularly simple manner, with considerable cost savings being achieved, in particular in the case of series products, by eliminating the previously required individual threshold setting for each copy .

Advantageous further developments and improvements of the method specified in claim 1 are possible through the measures listed in the subclaims.

The storage of the determined peak value is particularly advantageous, so that longer pauses between two successive wiping processes are possible.

A further advantageous measure is that when the windshield wiper is put into operation by a person, the peak value is initially not stored until the wiping process triggered for the first time begins.

A high level of interference immunity is achieved by pulsed operation of the radiation source.

The device according to the invention contains a detector which determines the peak value of the signal emitted by the radiation receiver.

In an advantageous embodiment of the device according to the invention, a phase-sensitive demodulator for the signal emitted by the radiation receiver is provided, which is controlled as a function of the pulse signal for operating the radiation source. A low pass is preferably indicated in the signal path after the demodulator. orders, whose cut-off frequency is lower than the frequency of the pulse signal for operating the radiation source. The low pass smoothes the output signal of the demodulator. The influence of a constant light component is additionally eliminated by using a high-pass filter in the evaluation device.

In an evaluation device according to the invention implemented in analog circuit technology, a capacitor is particularly suitable for storing peak values. The capacitor is preferably wired in such a way that the time for storing a value is considerably shorter than the storage time for the peak value.

In an evaluation device according to the invention implemented as a digital circuit, the storage of the peak value can be easily implemented with digital components or with the aid of a computer program.

Further details and advantageous developments of the method according to the invention and the associated device result from further subclaims in connection with the following description.

drawing

FIG. 1 shows an embodiment of an apparatus for carrying out the method according to the invention and FIG. 2 shows an embodiment of a peak value detector according to the invention.

Description of the embodiments

FIG. 1 shows a radiation source 10, the radiation 11 of which is directed into a pane 13 using an optical element 12. The disc 13 has an outer surface 14 to be cleaned. The in the Radiation 11 extending with disk 13 forms a predetermined angle of incidence 16 with a surface normal 15 to the disk surface 14. The angle of incidence 16 is fixed such that total reflection of the radiation takes place at a first point 17 on the disk surface 14. The reflected beam forms with the surface normal 15 an angle of reflection 18 which is equal to the angle of incidence 16. The reflected radiation is reflected again on an inner pane surface 19, with a total reflection taking place again. The radiation is reflected several times by multiple reflection on the outer and inner pane surfaces 14, 19 until it is coupled out of the pane 13 with an optical component 20 and fed to a radiation receiver 21. On the outer pane surface 14 there are water drops 22-25, which a wiper (not shown in FIG. 1) is intended to remove. Two water drops 23, 25 are drawn in at a second and third point 26, 27 on the outer pane surface 14, at each of which a reflection of the radiation 11 takes place. The higher refractive index of the water drops 23, 25 compared to the surrounding air leads to the fact that instead of a total reflection, a normal reflection takes place at the points 26, 27, in which a certain radiation component from the disk 13 into the water drops 23, 25 is decoupled and released from there into the environment. The lost radiation portions coupled out by the water drops 23, 25 are provided with the reference numbers 28 and 29, respectively.

The radiation source 10 is controlled by a pulse generator 40, the output signal of which is also a first input signal 41 of a phase-sensitive demodulator 42. The signal 43 emitted by the radiation receiver 21 is processed by an amplifier 44, which is preceded by a high-pass filter 45, and fed to the phase-sensitive demodulator 42 as a second input signal 46. After filtering in a low-pass filter 47, the output Signal of the demodulator 42 on the one hand to a first input 48 of a comparator 49 and on the other hand to a first input 50 of a peak value detector 51. A second input signal 52 of the peak value detector 51 is provided by an input 53. The output signal of the peak value detector 51 is the second input signal 54 of the comparator 49, the output signal of which is fed to a windshield wiper control 55 which is connected to the input 53. The wiper control 55 switches on the wiper.

FIG. 2 shows a circuit diagram of the peak value detector with a memory circuit. The circuit arrangement according to FIG. 2 is an advantageous embodiment of the peak value detector 51 according to the invention shown in FIG. 1. In FIG. 2, those parts which correspond to those shown in FIG. 1 are provided with the same reference numbers. The first input signal 50 of the peak value detector 51 is fed to the non-inverting input of a differential amplifier 60, the output signal 61 of which is fed to a capacitor 64 via a diode 62 and a resistor 63. The differential amplifier 60 is fed back by connecting its inverting input to the diode 62. The arrangement described stores in capacitor 64 the peak value of a signal at input 50. The injection time is mainly determined by the value of resistor 63 and the value of capacitor 64. The capacitor 64 can be discharged in two ways. On the one hand, a discharge resistor 66 which can be switched against a mass 65 is provided, an electrically controllable switch 67 being provided, to which the second input signal 52 of the peak value detector 51 is supplied as a control signal. On the other hand, a circuit arrangement 69 containing an impedance converter 68 is provided for discharging the capacitor 64. The capacitor 64 is connected to the input 70 of the impedance converter. The exit 71 of the Impedance converter 68 is connected via a first resistor 72 to a circuit point 73, which is connected to capacitor 64 via a second resistor 74 and to ground 65 via a third resistor 75. Instead of ground 65, another circuit point that has a fixed potential is also suitable. The impedance converter 68 is preferably implemented as a differential amplifier, which is completely negative-coupled in that the output 71 is connected to the inverting input of the differential amplifier.

The method according to the invention is explained in more detail using the arrangement shown in FIG. 1:

The radiation 11 emanating from the radiation source 10 arrives at the radiation receiver 21 after repeated total reflection in the pane 13. In order for total reflection to take place, the angle of incidence 16 of the radiation 11 with respect to the surface normal 15 must exceed a certain value, that of the material the disc 13 and on the medium surrounding the disc 13 depends. The minimum value of the angle of incidence 16 for a glass pane 13 which is surrounded by air is approximately 42 °. The radiation receiver 21 emits a signal 43 which is at a maximum with a clean pane surface 14. Wetting the surface 14 with water drops 22-25 leads to a decrease in the signal 43. The signal decrease results from the fact that the water drops 23, 25, which are located at the second and third points 26, 27, form part of the radiation 11 uncouple. After further refraction, the radiation 11 coupled into the water drops 23, 25 reaches the surroundings as loss radiation 28, 29. A beam is decoupled because the refractive index of water is higher than that of air, the angle of incidence 16 being increased for total reflection. Total reflection now occurs at an angle of incidence 16 that is more than about 63 °. The angle of incidence 16 is therefore expediently set to a value between approximately 42 ° and 63 °. The signal 43 emitted by the radiation receiver 21 passes into an evaluation device which contains, for example, an amplifier arrangement 44 with an upstream high-pass filter 45. The high-pass filter 45 removes any DC components from the signal 43 which may be caused by ambient radiation. A considerable increase in interference immunity is achieved if the radiation source 10 is operated in a pulsed manner. A pulse generator 40 is therefore provided, the output signal of which is supplied on the one hand to the radiation source 10 and on the other hand to the first input 41 of the phase-sensitive demodulator 42 as a reference signal. The input 46 of the phase-sensitive demodulator 42 receives the processed signal 43 emitted by the radiation receiver 21. The demodulator 42 ensures that only those radiation components received that are in phase with the emitted pulsed radiation 11 are used for evaluation. In addition to suppressing the constant light component, pulse signals which are not in phase with the emitted pulsed radiation 11 are thus also suppressed.

After signal filtering with the low-pass filter 47, the signal reaches the first input 48 of the comparator 49 and the first input 50 of the peak value detector 51. The peak value detector 51 determines the maximum of the processed signal 43 emitted by the radiation receiver 21. The maximum then becomes fed to the second input 54 of the comparator 49. The maximum determined by the peak value detector 51 is a reference value which corresponds to a clean pane surface 14. During a cleaning process of the pane surface 14, the surface 14 is at least briefly clean. The peak detector 51 must therefore detect the peak in this short, available time. This time should be less than 100 ms, preferably less than 10 ms. The peak determined is preferred saved during a subsequent cleaning break so that it is still available as a reference value. The storage time should be at least 100 s, preferably at least 1000 s. The maximum storage period depends on the maximum cleaning break to be bridged.

The use of the peak value detector 51 ensures that assembly uncertainties, for example the optical components 12, 20, copy variations of electronic components, in particular the electro-optical 10, 21, and long-term and temperature drift of all components are automatically taken into account in the method according to the invention. It is a particular advantage that the aging of the pane surface 14, for example an increase in scratches, also has no influence.

The comparator 49 then outputs a signal to the wiper control 55 when the two input signals 48, 54 exceed a predetermined difference, which may depend on the switch-on state of the wipers. Exceeding the predetermined difference means that the contamination of the pane surface 14 has exceeded a level that requires cleaning. The difference is determined experimentally and set in the comparator 49. The difference determination only has to be carried out once for series products. The wiper control 55 switches a wiper motor on or off depending on the signal emitted by the comparator 49 and on the other hand on the signal emitted by the input 53. The input 53 is, for example, a conventional windshield wiper switch, which is supplemented by a further switching position for automatic operation, or in which the interval operation is replaced by the operation according to the invention. An advantageous development of the method according to the invention is the measure that when the windshield wiper is put into operation by a person for the first time, the input 53 does not store the peak value in the detector 51 until the wiping process triggered for the first time begins.

In a further advantageous embodiment of the device according to the invention, instead of the high-pass filter 45 and the demodulator 42, a bandpass filter with a rectifier is provided. The center frequency of the bandpass is largely matched to that of the pulse generator. The bandwidth is adapted to the highest significant signal frequency. To smooth the rectifier signal, use a low-pass filter whose limit frequency is less than the pulse generator frequency.

The mode of operation of the peak value detector 51 according to the invention and the peak value storage is explained in more detail using the circuit arrangement according to FIG. 2:

The differential amplifier 60 and the diode 62 operate in a known manner as a peak value detector, at the output of which approximately the peak value of the signal occurring at the input 50 is present. The peak value is loaded into the capacitor 64 via the resistor 63. The value of the resistor 63 and that of the capacitor 64 are determined such that, starting from the discharged state of the capacitor 64, 2/3 of the peak value to be stored is reached at the latest after 100 ms, preferably less than 10 ms.

A first possibility of discharging the capacitor 64 is via the resistor 66 and the controllable switch 67 to ground 65. Resistor 66 limits the maximum discharge current. The controllable switch 67 is activated by the input 53 shown in FIG. 1 - left

controlled by briefly closing it, for example when a person wakes up the windscreen wiper for the first time, until the wiping process triggered for the first time begins. The switch 67 also offers a simple reset option in order to delete the stored peak value. This option is advantageous if an unusable peak value has been stored due to a malfunction of the circuit.

A further possibility for changing the peak value stored in the capacitor 64 is given by the circuit arrangement 69, which acts like a high-resistance discharge resistor. With the circuit arrangement 69, the discharge time of the storage capacitor 64 is determined such that a stored value has dropped to 2/3 of its original value at the earliest after 100 s, preferably 1000 s. An ohmic resistor cannot be used at this point, since its value would have to be a few gigohms, which in this application would not be economically feasible with the required reliability and long-term stability. In addition, there is the problem that the insulation resistance between the capacitor connections must be at least as great. The impedance converter 68 impresses a low voltage in the circuit point 73 via the resistor 72 as a function of the stored peak value. By specifying a small voltage difference between the stored peak value and the voltage at the switching point 73, the resistor 74 can be chosen to be relatively low-resistance. Resistor 75 can also be low-resistance due to the low-resistance connection to the rest of the circuit. Although only comparatively low-resistance resistors 72, 74, 75 are present in the circuit arrangement 69, the equivalent resistance of the circuit arrangement 69 lying between the capacitor 64 and ground has the required high value. If a shield ring is placed around the capacitor 64 and connected to the circuit point 73, insulation resistances in the order of magnitude of the resistor 74 are also sufficient. In a further exemplary embodiment of the device according to the invention for carrying out the method, the evaluation device shown in FIG. 1 for the signal 43 emitted by the radiation receiver 21 is implemented as a digital circuit, preferably with a microprocessor. After an analog-digital conversion of the signal 43 or the demodulated signal, the further signal processing takes place in the computer. The analog circuit of the peak value detector 51 shown in FIG. 2 is replaced in this exemplary embodiment either by digital components which are contained, for example, in the microprocessor or by a computer program, the advantage being that the peak value stored in a memory of the microprocessor is arbitrary can be stored for a long time.

Claims

Expectations

1. Method for operating a windshield wiper with the following features: a) the radiation of at least one radiation source (10) is into a windshield (13) at a predetermined angle (16) with respect to a surface normal (15) on an outer windshield surface to be cleaned by a windshield wiper (14) coupled; b) the angle (16) is chosen such that total reflection of the radiation (11) only takes place on the outer pane surface (14) when the surface (14) to be cleaned is not contaminated; c) the radiation (11) reflected on the outer and on an inner pane surface (14, 19) is coupled out and fed to a radiation receiver (21); d) the signal (43) emitted by the radiation receiver (21) is fed to an evaluation device in which the signal (43) is compared with a threshold; e) a cleaning process of the windshield wiper is triggered when the signal (43) emitted by the radiation receiver (21) exceeds the threshold by a predeterminable difference; characterized in that f) the threshold is tracked as a function of the peak value of the signal (43) emitted by the radiation receiver (21).

2. The method according to claim 1, characterized in that the peak value determined by the peak value detector (51) is stored.

3. The method according to claim 2, characterized in that when the windshield wiper is put into operation by a person via an input (53) the peak value is not stored until the cleaning operation of the windshield wiper initiated for the first time.

4. The method according to claim 2, characterized in that the stored peak value can be erased.

5. The method according to claim 1, characterized in that the radiation source (10) is operated in a pulsed manner.

6. The method according to claim 1, characterized in that the angle (16) to a value between 42 ° and 63 ° with respect to the Scheibennor¬ paint (15) is predetermined.

7. The method according to claim 1, characterized in that the threshold is chosen equal to the peak value.

8. Device for performing the method according to one of claims 1 to 7, characterized in that a phase-sensitive demodulator (42) is provided in an evaluation device for processing the signal (43) emitted by the radiation receiver (21) which is controlled as a function of the signal emitted by a pulse generator (40) for operating the radiation source (10).

9. The device according to claim 8, characterized in that the demodulator (42) is followed by a low-pass filter (47) whose cut-off frequency is less than the frequency of the signal emitted by the pulse generator (40) for operating the radiation source (10).

10. The device according to claim 8, characterized in that the signal emitted by the radiation receiver (21) (43) is fed to a high-pass filter (45).

11. The device according to claim 8, characterized in that a bandpass filter is provided in the evaluation device, whose Mitten¬ frequency corresponds approximately to the frequency of the pulse generator (40) and whose bandwidth corresponds to the highest significant signal frequency.

12. The apparatus according to claim 8, characterized in that a peak detector (51) is provided for determining the peak value of the signal (43) emitted by the radiation receiver (21).

13. The apparatus according to claim 12, characterized in that a storage capacitor (64) is provided for peak value storage.

14. The apparatus according to claim 13, characterized in that the charging time of the storage capacitor (64) is set such that, starting from the discharged state, at the latest after 100 ms, preferably less than 10 ms, about 2/3 of a spit ¬ protective peak are reached.

15. The apparatus according to claim 13, characterized in that the discharge time of the storage capacitor (64) is determined such that a stored value at the earliest after 100 s, preferably at the earliest after 1000 s, to about 2/3 of its original value is.

16. The apparatus according to claim 15, characterized in that for discharging the storage capacitor (64), a circuit arrangement (69) is provided which ent ent least at least one impedance converter (68).

17. The apparatus according to claim 16, characterized in that a) the storage capacitor (64) is connected to an input (70) of the impedance converter (68) and that b) the output of the impedance converter (68) with a resistor (72) is connected to a circuit point (73) which is connected to the storage capacitor (64) via a resistor (74) and to circuit ground (65) via a further resistor (75).

18. The apparatus according to claim 8, characterized in that the evaluation device is implemented as a digital circuit with a microprocessor which processes the signal (43) converted into a digital signal.

19. The apparatus according to claim 18, characterized in that the peak value is stored in a memory of the microprocessor for at least 100 s, preferably at least 1000 s.

20. The apparatus according to claim 18, characterized in that the peak value is stored in a memory of the microprocessor in less than 100 ms, preferably in less than 10 ms.