DE102014214414B3 - Ultrasonic sensor for detecting a piston in a cylinder - Google Patents

Abstract

Ultrasonic sensor for detecting a piston 1 in a cylinder 2 with an externally mounted on the cylinder ultrasonic transducer 3 and an evaluation unit 4 for generating a binary switching signal, the ultrasonic transducer 3 emits a transmission signal 5 and receives an echo signal 6, the evaluation unit 4, the echo signal 6 evaluates and a binary switching signal is generated, wherein the evaluation is carried out by comparing the current echo signal 6 with a known waveform, wherein the echo signal 6 is measured N times in at least two known piston positions, wherein a selected from the N measurements number of n measured values each form a prototype vector in which a signal vector having n measured values is formed from a current echo signal 6, wherein the similarity of the current signal vector to all prototypes is evaluated and a binary switching signal is generated as a function of this evaluation.

Description

The invention relates to an ultrasonic sensor for detecting a piston in a cylinder according to the preamble of patent claim 1.

The most common measurement method for detecting the piston position is certainly the magnetic. It works safely and reliably, but requires the magnetization of the piston or the attachment of a magnet in or on the piston and fails in ferromagnetic cylinder walls.

In these cases, the also known for a long time ultrasound measurement, which requires only a slightly later to be attached to the outer cylinder wall ultrasonic transducer (transducer) and a somewhat more complicated electronic evaluation circuit.

The DE 10 2005 005 965 A1 shows an ultrasonic sensor to be attached to the outer cylinder wall, which emits individual ultrasonic pulses with a resonant frequency between 250 kHz and 4 MHz, which propagate through the cylinder wall and the medium therein and are reflected by the opposite wall.

The evaluation unit includes an adjustable amplifier and a comparator for comparing the reflected signals with a threshold value.

The surface area of two temporal expectation ranges, whose time interval to the ultrasound pulses must be set as a function of the cylinder diameter, is evaluated, the time range in question being approximately 5000 .mu.s.

On the one hand, the required manual adjustment of the time range and the associated use of qualified specialist personnel and, on the other hand, the insufficient distinguishing power of the envelopes in the piston positions to be detected are regarded as disadvantageous.

The DE 10 2007 062 782 A1 shows a similar arrangement, wherein the evaluation of the received ultrasonic signal is carried out by comparing the waveform of the envelope with a stored in the device reference curve. For this purpose, the ultrasonic signal is digitized and subjected to the resultant result vector of a correlation analysis.

The problem here is sometimes in some cases, especially for distinguishing multiple piston positions and complex cylinder geometries, not always sufficient distinctiveness.

The object of the present invention is to further improve the state of the art. In particular, several piston positions are to be distinguished with greater certainty.

This object is achieved with the characterizing features of claim 1. The dependent claim relates to the advantageous embodiment of the invention.

The essential idea of the invention consists in detecting the echo signal in at least two known piston positions with N sampling points and in each case forming a prototype vector with a number of n measured values selected from the N values, each piston position corresponding to a prototype. These prototype vectors can be entered or taught in and stored in the ultrasonic sensor.

For the measurement, a signal vector with n measured values is formed from the current echo signal and the most similar prototype vector is selected. Depending on the selected prototype, a binary switching signal is generated. Of course, the position of the most similar prototype can also be output.

In an advantageous embodiment, to select the prototype, the signal vector of at least two prototype vectors present is subtracted, the amounts of the resulting difference vectors are mapped as coordinates into a feature space, the dimension of the feature space corresponding to the number of piston positions to be detected, and the prototype by classification in at least two-dimensional feature space selected.

The advantage of the invention is that several piston positions can be better distinguished.

The invention will be explained in more detail with reference to the drawing.

1 shows the ultrasonic sensor according to the invention in a schematic representation.

2 shows the difference vectors resulting from subtraction of signal and prototype.

3 shows the classification according to the invention in the two-dimensional feature space.

The 1 shows the ultrasonic sensor according to the invention in a simplified schematic representation. The device is on the outside of a cylinder 2 arranged.

At the front of the ultrasonic sensor is an ultrasonic transducer 3 arranged, which is connected via a switch with a transmission stage S or a receiving amplifier E. The switch is from a to a control and evaluation 4 belonging microcontroller μC controlled, which includes a generator G for generating transmission pulses and an analog / digital converter A / D for digitizing the received signals. The signal forms are indicated at the input of the transmit amplifier S and at the output of the receive amplifier E. Furthermore, control and display elements, an internal voltage stabilization and two antivalent switching outputs are shown. It should be noted here that the ultrasonic transducer 3 also in two parts with separate transmit and receive transducers or without a switch, or can be operated with constantly active receive amplifier E. In the latter case, the overdriving of the receiving amplifier E is to be countered. As an ultrasonic transducer 3 is preferably a piezoelectric element. Apart from those shown, further optical display elements, a bus interface or even digital or analog outputs can be present.

The 2 shows four difference vectors due to the subtraction of signal vectors and prototype vectors for two piston positions.

At the top left is the difference between a first prototype vector for the prototype "piston present" and a signal vector measured for this situation. The differences are expected to be the lowest. The sum over all difference values is therefore correspondingly small. In a possible implementation, this is about 2.5 mV.

At the top right is the difference between said first prototype vector and a second signal vector measured when the piston is absent. In this case, the difference is expected to be much higher. Here the sum over all difference values is approx. 15 mV.

At the bottom left is the difference between a second prototype vector, this time for the prototype "piston absent", and a typical signal vector for the present piston. Here the sum over all difference values is approx. 13 mV.

Bottom right is the difference between the second prototype vector, i. again shown for the prototype "piston absent", and a measured signal vector at absent piston. Here the sum over all difference values is approx. 6 mV.

Of course, here is the sum of the amounts of the difference values, the root of their sum of squares or a similar magnitude independent of the sign to consider.

The 3 shows the classification according to the invention in a two-dimensional feature space. The abscissa and the ordinate are spanned by the vectorial differences of the two prototype vectors and the signal vectors.

Here, the sum of the differences (first prototype vector - first signal vector) the abscissa and the sum of the differences (second prototype vector - second signal vector) is the ordinate.

Each new prototype would extend the classification space by one dimension. The absolute amounts of the differences between the prototype vector and the signal vector give the coordinates. With the above numerical values you get the in the 3 displayed, authentic measured values.

The distances to the prototype vectors are on the order of 10 to 20 mV and thus allow a comparatively safe decision on the presence of the piston 1 ,

LIST OF REFERENCE NUMBERS

1

 piston

2

 cylinder

3

 ultrasound transducer

4

 Control and evaluation unit

5

 send signal

6

 echo signal

Claims (2)

Ultrasonic sensor for detecting a piston ( 1 ) in a cylinder ( 2 ) with an outside of the cylinder mounted ultrasonic transducer ( 3 ) and an evaluation unit ( 4 ) for generating a binary switching signal, wherein the ultrasonic transducer ( 3 ) a transmission signal ( 5 ) and an echo signal ( 6 ), the evaluation unit ( 4 ) the echo signal ( 6 ) and generates a binary switching signal, wherein the evaluation by comparing the current echo signal ( 6 ) takes place with a known signal characteristic, characterized in that the echo signal ( 6 ) is measured N times in at least two known piston positions, wherein a number of n measured values selected from the N measurements each form a prototype vector, whereby a current echo signal ( 6 ) a signal vector is formed with n measured values, wherein the similarity of the current signal vector to all prototypes is evaluated and a binary switching signal is generated as a function of this evaluation. Ultrasonic sensor according to claim 1, characterized in that for the selection of the prototype of the current signal vector is subtracted from the at least two prototype vectors, the sums of the difference values resulting from the vectorial subtractions are mapped as coordinates in a feature space, wherein the dimension of the feature space of the number of corresponds to detecting piston positions, and the prototype is selected by a classification in the at least two-dimensional feature space.

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