DE102014103705B4 - Location system for securing a danger zone around mobile machines - Google Patents

Abstract

A system for securing an area around a work machine (1), comprising: - at least two loudspeaker units (5p) arranged on the work machine (1); At least one base station (3) arranged on the work machine (1) and designed to generate transmit signals which are supplied to the loudspeaker units (5p) and emitted as acoustic signals in the audible audio frequency range, the base station (3) comprising a first Radio module (4); - At least one handset (8) with a second radio module (7) and at least one microphone unit (6) for receiving the radiated acoustic signals; wherein: the transmit signals are hyperbolic frequency modulated chirp signals having a specific pulse duration (Ts) and a start frequency and a stop frequency; - The base station (3) is further adapted to transmit with the aid of the two radio modules (4, 7) a synchronization signal to the mobile part (8) and synchronous to the synchronization signal to generate the transmission signals for the speakers (5p); - The handset (8) is adapted to receive the synchronization signal and in synchronism with the synchronization signal from the speakers (5p) emitted acoustic signals and to determine a signal delay (τp) for each transmit signal; and - base station (3) or handset (8) or both are designed to calculate from the determined signal propagation times (τp) the relative position of the mobile part (8) relative to the work machine (1) and dependent on the calculated relative position on the initiation to decide on security measures.

Description

Technical area

The invention generally relates to a location system for detecting persons within a danger zone around a mobile work machine, for example a rock drilling machine in mining and tunneling.

Technical background

In many areas, such as mining and tunneling, workers are close to large, mobile work machines. In order to ensure the safety of persons or to avoid accidents, persons (or objects) in certain situations (e.g., when the work machine is in motion) should maintain a safe distance from the work machine, ie, not enter a defined danger zone around the work machine.

Various systems are known which determine the position of a person relative to a work machine and issue a warning when it is detected that a person is within a defined danger area. Such systems for locating persons in a danger zone must comply with certain guidelines or standards (eg ATEX in Europe) in different countries and be certified if necessary. In a publication (Randell, Muller - Low Cost Indoor Positioning System) of the Department of Computer Science, University of Bristol, UK, a system is presented, which allows a cost-effective location in closed spaces to realize. DE 32 08 901 A1 describes a method and apparatus for preventing collision accidents between work machines and persons. DE 10 2009 031 955 A1 describes a location system for spatial position determination by means of ultrasound.

In particular, when used underground, such positioning systems must be designed very robust. Locating systems that will use electromagnetic signals may be affected by the presence of solid metal (heavy machinery, tunnels, ore deposits, etc.). Systems using acoustic signals (auditory sound, ultrasound) must operate reliably despite a relatively high noise level. Consequently, there is a need for a (in terms of robustness) improved system for detecting persons or objects in the vicinity of mobile work machines.

Summary of the invention

A system for securing an area around a work machine is described. According to one example of the present invention, the system has at least two loudspeaker units arranged on the work machine and at least one base station arranged on the work machine with a first radio module. The base station is configured to generate transmit signals that are supplied to the speaker units and emitted as acoustic signals in the audible audio frequency range, wherein the transmit signals are hyperbolic-frequency modulated chirp signals having a specific pulse duration and a start frequency and a stop frequency. The system further comprises at least one handset with a second radio module and at least one microphone unit for receiving the radiated acoustic signals. The base station is further configured to transmit a synchronization signal to the mobile part with the aid of the two radio modules and to generate the transmission signals for the loudspeakers synchronously with the synchronization signal. The mobile part is designed to receive the synchronization signal and synchronously to it the acoustic signals radiated by the loudspeakers and to determine a signal delay time for each transmission signal. Base station or handset or both together are designed to calculate the relative position of the handset relative to the work machine from the determined signal propagation times and to decide depending on the calculated relative position on the initiation of security measures.

Brief explanation of the illustrations

The invention will be explained in more detail with reference to the examples shown in the figures. The illustrations are not necessarily to scale and the invention is not limited to the aspects presented. Rather, emphasis is placed on representing the principles underlying the invention.

1 shows a schematic representation of an example of the system according to the invention;

2 shows the system 1 using a block diagram;

3 shows the flow of a measuring cycle on the basis of a flow chart;

4 schematically shows the position of a handset relative to the base station;

5 schematically shows the components of the control circuit for controlling the signal-to-noise ratio;

6 shows a block diagram of the 5 belonging control loop.

In the figures, like reference characters designate like or corresponding components of same or similar meaning.

Detailed description

The examples of the invention described herein are described in the context of work machines used in mining and tunneling. However, other applications of the invention, for example in road construction, are also possible. In 1 is an example of a system according to the invention for the detection of persons or objects in the vicinity of a work machine sketched. In the in 1 As shown, the mobile work machine is a mining machine 1 (Tunneling machine, large drilling machine, etc). Sketched is also a person 2 near the machine. The location system described here is designed to be the person 2 to locate and detect whether this is within a (freely definable) danger zone. Depending on the result of this detection, warning signals may be issued or other safeguards may be initiated. In 2 is the system off 1 abstract illustrated by a simplified block diagram.

At the mobile work machine 1 is a base station 3 arranged with a radio module 4 connected is. Furthermore, at the work machine 1 three or more speaker units 5 arranged by the base station 3 be controlled. Each speaker unit 5 includes one or more speakers. One (or each) person to be detected 2 carries on the body a handset 8th , which also has a radio module 7 connected is. Furthermore, the person wears 2 at least one microphone unit 6 on the body. In the in 1 shown example, this is the helmet of the person 2 attached. The microphone unit 6 includes at least one microphone and may further comprise a preamplifier for amplifying the microphone signal (or the microphone signals). The microphone signal (s) is (are) the handset 8th fed and processed there. According to one example of the invention, the microphone unit comprises 6 three by 120 ° to each other angularly arranged microphones whose output signals are added. The microphones are arranged in such a way that no destructive interference occurs in the relevant frequency range (ie in the frequency band of the transmission signals). The functioning of the in the 1 and 2 The system shown in the following is based on the flow diagram in 3 explained in more detail.

The position measurement can be carried out continuously, for example at regular time intervals (measuring cycles). At the beginning of each measurement cycle, the base station transmits 3 with the help of the radio module 4 a synchronization message from the handset 8th with the help of the radio module 7 Will be received. A defined delay time (theoretically could be zero) after the synchronization message is given by means of the loudspeaker units 5 several acoustic locating signals emitted (see 3 , Step 21 ). The speaker units 5 are doing so at known positions on the mobile machine 1 arranged. The location signals may be from the handset 8th with the help of at least one microphone unit 6 or another transducer can be received and evaluated (see 3 , Step 23 ).

To determine the duration of the acoustic locating signals is in the handset 8th the scanning of the microphone unit 6 received signal when a synchronization message is received from the base station (see 3 , Step 22 ). The sampling of the received signal is thus synchronous to the synchronization message, wherein the signal propagation time of the radio-transmitted synchronization message can be neglected. Due to the extremely different propagation speeds of electromagnetic (radio) and acoustic (sound) waves to the received acoustic localization signals of the respective dispatch time (approximately time of sending the synchronization message) is known and the term ("time of flight") of the locating signals can be determined be (see 3 , Step 24 ). For each received locating signal, the transit time corresponds to the time difference of the sending time (signaled by the synchronization message) and the receiving time. In each measurement cycle, the runtimes are transmitted by radio from the handset 8th to the base station 3 transfer. The base station 3 is adapted to the received data from the relative position and the relative speed of the handset (relative to the machine 1 ) (see 3 , Step 25 ). The measured transit times can be converted into distances using the known speed of sound. The base station can take into account the temperature dependence of the speed of sound by means of a temperature measurement in order to improve the accuracy of the measurement.

Depending on the determined relative position and possibly also on the relative speed, safeguards can be initiated. In the simplest case, an optical and / or acoustic alarm signal is triggered. However, also a (partial) emergency shutdown of the working machine 1 respectively. As mentioned, the measuring cycles can take place at regular intervals, but asynchronous (eg event-triggered) measuring cycles can also be triggered.

In the example described below, hyperbolic frequency modulated chirp signals are used. Chirp (chirp) generally refers to signals whose frequency changes over time. Basically, the use of other (chirp) waveforms is possible, but characterized hyperbolic-frequency-modulated chirp signals in that the term estimation using a cross-correlation (which can be calculated, for example, on the cross-power density spectrum in the frequency domain) is relatively robust in terms of - a relative movement between transmitter (base station 3 ) and receiver (handset 8th ) - Doppler shift of the spectrum of a locating signal. In contrast, the Doppler shift causes, for example, linear frequency-modulated chirp signals distortion of the correlation signal and thereby a systematic error in the transit time measurement. A hyperbolic-frequency-modulated chirp signal s _HFM (t) can be described by the following equation: s _HFM (t) = w (t) · sin (2π / b · ln (1 + bf ₁ t)), (1) in which

Here, f _{0 is} the start frequency and f _{1 is} the stop frequency of the chirp signal, T _S denotes the duration of the chirp signal (chirp pulse) and w (t) is a (eg rectangular) window function. For an up-chirp (increasing frequency) f ₁ > f ₀ , for a down-chirp (falling frequency) f ₀ > f ₁ . To convert signal propagation times into distances, the speed of sound c ₀ is modeled as follows: c ₀ = 331.5 m / s + 0.6 m / s · K · (θ - 273.15 K), (3) where θ represents the ambient temperature in Kelvin.

About each speaker unit (see 2 , Reference number 5 ), another locating signal s _HFM (t) is emitted, the locating signals differing by their start and stop frequencies f ₀ , f ₁ . In the example described here, the bandwidth of a locating signal is 5 kHz each, and there are six loudspeaker units 5 used. The starting frequencies f _{1 of} the respective chirp signals are 1500 Hz, 1937.5 Hz, 2375 Hz, 2812.5 Hz, 3250 Hz and 3687.5 Hz. However, these numerical values are only to be understood as examples and may be chosen differently depending on the application , In order to compensate for the mentioned Doppler shift, a chirp pair is emitted simultaneously, namely an up-chirp (with increasing frequency) and a down-chirp (with decreasing frequency), the start or stop frequencies of both chirps coinciding (starting frequency of the Up chirp is equal to the stop frequency of the down chirp and vice versa). So k different chirp pairs are transmitted, where k is the number of speakers 5 is. In the present example, k = 6. The pulse duration is, for example, 360 ms. The actual value can also be chosen differently depending on the application. The individual speakers will be included in the episode 5 _p , where p = 1, 2, ..., k. The frequency ranges of the chirp signals are in the example described here above 1500 Hz. Especially in applications underground, relatively strong noise levels are to be expected in the low-frequency range below 1500 Hz.

As soon as the synchronization message has been received (see step 22 ), the timing is started and that of the microphone unit 6 generated signal s _R (t) is for a certain recording time T _R (digital) recorded. With a sample rate of 32kHz and a recording time of T _R = 512 ms, 2 ¹⁴ = 16384 readings are taken in one cycle. Said recording time T _R allows a measurement up to a distance of about 50 m (at T _R = 512 ms and T _S = 360 ms).

The recorded digital signal s _R (t) is now correlated with the k chirp pairs. Thus, 2k cross-correlation signals are calculated, which is conveniently achieved in the frequency domain using a Fast Fourier Transform (FFT) algorithm. Each chirp is therefore assigned a correlation signal. Ideally, the transit time of a chirp signal can be determined from the (temporal) position of the maximum in the associated correlation signal. Especially in the application underground (ie in tunnels and tunnels), however, it can lead to strong reflections and overlays, so that acoustic signals that do not directly from a speaker to the microphone reach (so-called "non-line-of-sight signals" ), a higher correlation maximum result as acoustic signals, which come directly from a speaker to the microphone (so-called "line-of-sight signals").

The 2k correlation signals are fed to an analysis unit which is designed to search in each of the 2k correlation functions those maxima ("correlation peak") whose value is above a certain threshold value s _TH . The threshold value can be selected depending on the respective correlation signal. For example, the threshold value s _{TH is} a multiple of the median used as a measure of the existing noise of the relevant correlation function. The thus found maxima (correlation peaks) serve as a basis for determining the position in which the maxima are evaluated and selected. The global maximum (the highest peak) does not necessarily correspond to that acoustic signal, which is the direct path between transmitter (loudspeaker 5 _p ) and receiver (microphone unit 6 ) took. By superimposing the direct sound with echoes, the global maximum is not always the temporally first local maximum in the calculated correlation signal. To find the local maximum corresponding to the acoustic signal which has taken the direct path between transmitter (loudspeaker) and receiver (microphone), different algorithms can be used. For example, the global maximum of the correlation signal is first determined. On the basis of this global maximum, further local maxima are investigated, which occur temporally in the correlation signal at an earlier point in time and have a fixed minimum height in relation to the global maximum. From these further maxima, for example, the earliest earliest possible propagation time of the direct signal can be assumed. This selected maximum is assigned a physical time of arrival (TOA).

In the manner described above, 2k arrival times (TOA) are obtained, which are marked with t _{q, p} (where p = 1, ... k, and q = 1 for up-chirp and q = 2 for down-chirp). From these arrival times, can then be p for each chirp pair or for each speaker 5 _p an estimated time of flight τ _p ("time of flight", TOF) and, in turn, an estimated distance d _p and an estimated radial velocity v _p . From the individual distances d _p and the individual radial velocities v _p , the relative position and the relative speed of the person 2 that the handset 8th in itself, based on the working machine 1 be determined. This situation is - for p = {1, 2, 3, 4} - in 4 shown. For each chirp pair (for each speaker 5 _p ), the transit time τ _{p is determined} as the mean value of the two corresponding arrival times t _{p, 1} , t _{p, 2} of up or down chirp, minus a correction term which depends on the difference t _{p, 1} -t _{p, 2} compensated for the influence of the Doppler shift. The calculated relative velocity can be used to more accurately calculate the relative position and relative velocity in the next time step.

When used underground (in tunnels or tunnels), the ambient noise level can fluctuate greatly and at times be relatively high. The handset 8th must, with the help of the microphone unit 6 However, an acoustic signal of sufficient quality (sufficient signal-to-noise ratio SNR) received in order to perform the above-described distance estimation reliable. For this purpose, the handset 8th (or the microphone unit 6 of the handset 8th ) is adapted to calculate a measure representing the current signal quality of the received chirp signals. For example, this measure is the signal-to-noise ratio. This measure is via the radio modules 4 and 7 to the base station 3 Posted. The base station 3 is thus able to control the volume of the speakers 5 _p to regulate emitted chirp signals. For example, if the signal-to-noise ratio (SNR) is too low, the volume can be increased to increase (increase) the SNR; if the SNR is higher than necessary, the volume of the chirp signals can be reduced to reduce the interference from the audible ones Keep chirp signals as low as possible. In this way a regulation of the SNR is possible.

In the 5 and 6 the principle of SNR control is shown schematically. For the sake of simplicity, is in 5 only one speaker 5 shown. The audible signal transmitted at an adjustable volume (signal power) is provided by the microphone unit 6 of the handset 8th received, and the handset is adapted to calculate the SNR and the currently calculated value using the wireless modules 7 and 4 to the base station 3 to convey. The base station 3 includes a signal processor 31 which is adapted (with the aid of suitable software) to generate the chirp signals and the gain of a subsequent amplifier 32 - And thus adjust the volume of the emitted chirp signals. 6 shows a control loop that is partially in the mentioned signal processor 31 is implemented. The (digital) SNR controller 310 generated from the difference of the current from the handset 8th SNR transmitted to the base station and a setpoint SNR _SET a volume control signal VOL, with which, for example, the gain of the amplifier 32 is set. This volume control signal VOL in turn has an influence on the SNR. The transmission behavior of volume control signal VOL to SNR is determined by the transfer function of the controlled system 800 represents. The controlled system includes the transmission behavior of the loudspeaker, the acoustic transmission path, the microphone and the SNR calculation in the handset 8th , With the aid of the illustrated control loop, the SNR can be regulated to a desired nominal value SNR _SET .

The area surrounding the work machine can be subdivided into warning and alarm zones. The base station 3 determines the position of a handset as explained above 8th and can check from the position determined whether the handset 8th within a warning or alarm zone. These alarm and warning zones can be defined as polygons, for example. If a handset is in a warning zone, a visual or audible alarm may be triggered as a safety measure. Is a handset in an alarm zone? 8th can a - at least partially - shutdown of the machine 1 be initiated. In particular, the work machine can be braked to a standstill.

Claims (10)

System for securing an area around a working machine ( 1 ), comprising: - at least two on the working machine ( 1 ) arranged speaker units ( 5 _p ); - at least one on the working machine ( 1 ) base station ( 3 ) which is adapted to generate transmission signals to the loudspeaker units ( 5 _p ) and are emitted as audible signals in the audible audio frequency range, the base station ( 3 ) a first radio module ( 4 ) having; - at least one handset ( 8th ) with a second radio module ( 7 ) and at least one microphone unit ( 6 ) for receiving the radiated acoustic signals; wherein: the transmit signals are hyperbolic frequency modulated chirp signals having a particular pulse duration (T _s ) and a start frequency and a stop frequency; - the base station ( 3 ) is further adapted, with the aid of the two radio modules ( 4 . 7 ) a synchronization signal to the handset ( 8th ) and in synchronism with the synchronization signal the transmission signals for the loudspeakers ( 5 _p ) to produce; - the handset ( 8th ) is adapted to the synchronization signal and synchronous to the synchronization signal from the speakers ( 5 _p ) to receive radiated acoustic signals and to determine a signal transit time (τ _p ) for each transmit signal; and - base station ( 3 ) or handset ( 8th ) or both are formed together from the determined signal propagation times (τ _p ), the relative position of the handset ( 8th ) related to the working machine ( 1 ) and decide on the initiation of safety measures depending on the calculated relative position.  A system according to claim 1, wherein as transmission signals for each loudspeaker certain chirp signals are generated, each differing in the start and stop frequencies.  System according to claim 1, wherein as transmission signals for each loudspeaker an up-chirp and a down-chirp are respectively generated, which are emitted simultaneously as acoustic signals, wherein the starting frequency of the up-chirp corresponds to the stop frequency of the down-chirp and vice versa.  A system according to any one of claims 1 to 3, wherein the transmission signals are audio signals in a frequency range of 1500 to 15000 Hz. System according to one of Claims 1 to 4, in which the base station ( 3 ) is adapted to the volume of the transmission signals depending on a measured value, the signal quality in the handset ( 8th ) represents received acoustic signals to adapt.  A system according to claim 5, wherein the measurement value representing the signal quality depends on a power of the received acoustic signal and on the power of the ambient noise. System according to Claim 5 or 6, in which the measured value representing the signal quality is received by the mobile unit ( 8th ) and transmitted to the base station.  The system of claim 5, wherein the handset is configured to determine the power of the ambient noise in a frequency range that is below the frequency range of the transmit signals, wherein the power of the received acoustic signals and the detected power of the ambient noise generate a signal-to-noise ratio. Ratio determined and transmitted to the base station via radio, and wherein the base station is adapted to adjust the volume of the transmission signals so that the resulting signal-to-noise ratio corresponds to a specific setpoint. System according to one of Claims 1 to 8, in which the microphone unit ( 6 ) for receiving the radiated acoustic signals comprises a plurality of microphones, in particular three mutually rotated by 120 ° to each other arranged microphones. System according to one of Claims 1 to 9, in which the area around the working machine is subdivided into warning and alarm zones and the base station ( 3 ) is designed to determine whether a handset ( 8th ) is located within a warning or alarm zone, with an alarm signal being issued as a safety measure when a handset is in a warning zone and as a safety measure initiating at least partial shutdown of the work machine when a handset is in an alarm zone.

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