Handheld laser distance measuring device using an impulse back-mixing method

p0001The invention refers to a laser distance measuring device with a hand pulse reflection mixing method, in particular a Baulaserdistanzhandmessgerät.

p0002In construction, the precise determination of the distance with an accuracy of a few mm is required at a range up to some 100m. The suitable trained laser distance handheld instruments to which this invention relates to use for distance measurement, a pulse reflection mixing method of a modulated visible laser beam.

p0003After <patcit id="pcit0001" dnum="DE10112833C1"><text>DE10112833C1</text></patcit> is known a laser distance measuring device with a hand pulse reflection mixing method. In such a pulse reflection mixing laser distance measuring devices Hand with a pulse reflection mixing method are used as laser sources commercially available laser diodes which emit in the visible red wavelength range. The emitted laser light is with a series of very narrow needle pulses - hereinafter referred to as transmission pulse sequence - modulated and bundled with a collimator lens to a measurement laser beam. This special pulse reflection mixing laser distance Hand device thus requires a transmission pulse sequence is a series of very narrow laser pulses with a width typically between 60 ps and 80 ps. The pulse repetition frequency of the laser pulses in the range of 50 MHz to 200 MHz is very high compared to the pulse repetition frequency of some 10 kHz with conventional pulse-laser distance handheld instruments, so that, for a determined fixed pulse repetition rate is generally a measurement to a few no clear determination of distance and the distance range 100m is possible. Thus, at least two measurements at two substantially different repetition rates or differences from pulse repetition frequencies are necessary for an unambiguous determination of distance, for very large distance ranges with high accuracy even more different. The control means determined by an algorithm which is generally non-unique time differences between the reference and measurement pulses of low frequency mixing pulse sequence at different repetition rates and from a system of equations using the speed of light, the unique distance from the distance meter to spot on the measurement object. Detected by the light detector reference pulse sequence on the one hand and the measuring pulse train on the other hand be subjected directly to a direct mixing and subsequent low-pass filtering in the light detector, the direct mixing is carried out by a locally generated at the measurement location Lokalozillatorimpulsfolge under control, the duty ratio of equal to or approximately equal to the duty cycle of the measurement pulse sequence and whose repetition frequencies slightly different are selected. The Mischimpulswiederholfrequenz the resulting low-frequency mixing pulse sequence therefore corresponds to the amount of the difference between the pulse repetition frequency of transmitting and measuring pulse sequence and the pulse repetition rate d he Lokalozillatorimpulsfolge. The time base is thereby stretched by a large factor (for example 1 million). The low-frequency mixed pulse sequence is as the high-frequency detecting pulse sequence (superposition of the measuring pulse sequence with the reference pulse train) from the frequency-converted reference and measurement pulses whose time offset is a measure of the distance. The low-frequency mixing pulse sequence with a small Mischimpulswiederholfrequenz, for example, less than 1 kHz is low pass filtered, amplified, sampled with an analog-digital converter and fed to the control means, which is the time difference between the frequency-converted reference and measurement pulses, and from this the (possibly not unique) distance to the measured object determines which is uniquely determined as described initially by multiple measurements with different pulse repetition frequencies. For further details concerning the generic laser distance Hand meter with a pulse reflection mixing method, the skilled person is referred to this document and incorporated the disclosure of which are hereby explicitly. In this method, two slightly different pulse repetition frequencies are used, the method heterodyne pulse backmixing is called. In such heterodyne methods continuously through all times a pulse period, although the information content is only at very short intervals, ie. At the points of reference and measurement pulses Since the reference and measurement pulses account for only a small percentage of the pulse period, frequency mixing, the measurement time is utilized only to a small extent.

p0004The object of the invention is to make better use of the measurement time during pulse reflection mixing method and thus in an increased sensitivity and range of the laser distance measuring device Hand.

p0005The object is achieved essentially by the features of claim 1. Advantageous developments emerge from the dependent claims.

p0006Thus, a pulse reflection mixing laser distance hand held instrument with a control means for calculating the distance to a measurement object by at least one identifiable, periodic with a pulse repetition frequency, time difference between a reflected on the DUT measurement pulse and a way past a reference path reference pulse of an optically radiated transmit pulse, a local oscillator for generating of the transmit pulse at the pulse repetition rate and at least one variable from the control means controllable delay circuit which is disposed between the local oscillator and a light detector and / or a light emitter, and generates a delay between the sampling pulses and the transmission pulses for sampling the measurement pulse and the reference pulse.

p0007The associated measurement method has within the calculation step of the distance from the at least one time difference between the measurement pulse and the reference pulse by the algorithm of the control means, at least one transit time determination step of determining the time difference between the measurement pulses and the reference pulses to, and within which a plurality of scanning steps which the received by the light detector and periodic in a pulse repetition rate measuring pulses and reference pulses to scan directly on the light detector with sampling pulses precisely this pulse repetition frequency and detect the scanning result from the control means, wherein the control means by means of the delay circuit is a delay between the sampling pulses and the transmission pulses is controlled, and in the overall duration determining step the time difference between the measuring pulses and the reference pulses of exactly correspond to the time delays is calculated, the sampling instants are associated with successful.

p0008In each case, under controlled deceleration equally the delay of the sampling pulses with respect to transmit pulses and the delay of the transmit pulses relative to the sampling pulses understood.

p0009By the measuring pulses and the reference pulses are sampled with the sampling pulses, the time delay controlled variable at the same pulse repetition frequency with respect to the transmission pulses is produced instead of a low-frequency mixing pulse sequence in a prior art heterodyne pulse trailing mixture at this inventive homodyne pulse backmixing a DC signal as a scanning result, which has a high amount, if the sampling pulses coincide in time with the measuring pulses or with the reference pulses. In the other case, the DC signal has a small amount or is zero. Thus, the temporal positions of the measurement pulses and the reference pulses are known within the pulse period the control means via the actively varied by the control means correct time, whereby frequent sampling for the detection of pulses at this time known positions can be generated by the control means, whereby the measurement time is better exploitable for detection.

p0010a second delay circuit is advantageously provided which is located between the local oscillator and a light transmitter for the transmission of the transmitted pulse, more advantageously with the first delay circuit different delay times, resulting in more possible combinations with respect to the unrealized delay times and thus the time resolution.

p0011Advantageously, (each) on an output of delay circuit (s) arranged pulse shaper available, resulting in a very short pulse width and thus short-term sampling is implemented, whereby the measuring accuracy is increased. In this case the (advantageously controllable) local oscillator need not be a (good) pulse generator itself. Further advantageously located respectively in front of the pulse shaper, a programmable frequency divider, which can generate pulse trains with controllable but identical repetition (with identical division).

p0012a connected to the control means phase detector advantageously is present, at the two inputs bear the transmitted pulses and the sampling pulses, thereby via the delay circuit (s) varied time delay measured and the correct operation of the delay circuit (s) is controllable.

p0013the delay circuit is advantageously embodied as a digital delay circuit, also advantageous as a fully integrated delay module, whereby this so the exact delay time is digitally controlled by the control means and adjustable.

p0014the light detector advantageously is an avalanche photodiode (APD), the reverse bias voltage is superimposed on the power supplied by the local oscillator sampling pulse train and which is used to homodyne pulse mixture, wherein the amplification factor of the avalanche photodiode in the blanking intervals of the sampling pulse is substantially lower than during the presence of sampling, thereby effecting a high-sensitivity scanning of received, weak light signals.

p0015the light detector advantageously is connected to a low-pass, which is further advantageously connected to an amplifier which is further advantageously connected to an analog-to-digital converter that is further advantageously connected to the control means, whereby the dc signal is fail-safe by the control means can be detected.

p0016the resulting sensing result is advantageously in the scanning first low-pass filtered in the form of an analog DC signal in the scanning step, then amplified and then sampled with an analog-digital converter and digital supplied to the control means.

p0017the measurement pulses and the reference pulses are advantageously in the duration determining step (not necessarily strictly alternating or uniform distribution) sampled temporally successive scanning, whereby the time delay is separately detected without interference to the transmission pulses.

p0018the sampled reference and measurement pulses are temporally correlated advantageous, whereby the time shift can be determined.

p0019the measurement pulses and the reference pulses are advantageous for the duration determining step repetitively sampled and averaged in several consecutive sampling steps, whereby their individual sampling results are accumulative and the time delay to the transmission pulses from the superposition of the sampling results through correlation robust determinable.

p0020the time differences of transit time determination steps are advantageously used with different pulse repetition frequencies for calculating the distance in the calculation step, whereby the uniqueness of the measure is granted even for large distances. Further advantageously, the pulse repetition frequency is adjusted or changed so that there is no overlap between the reference and measurement pulses takes place.

p0021The invention is relative to an advantageous embodiment explained in more detail with:<dl id="dl0001"><dt>Fig. 1</dt><dd>as a pulse reflection mixing laser distance meter Hand</dd><dt>FIG. 2</dt><dd>as an algorithm of the measurement method</dd></dl>

p0022After <figref idrefs="f0001">Fig. 1</figref> has a pulse reflection mixing laser distance Hand instrument 1 a control means 2 in the form of a microcontroller to calculate the distance D to a measurement object 3 via at least one detectable, with a pulse repetition rate f periodic, time difference between a reflected on the measurement object 3 measuring pulse 4 and a reference path 5 overflowed reference pulse 6 to an optically radiated transmit pulse. 7 In addition, a controlled local oscillator 8 for generating the transmission pulse 7 with the pulse repetition rate f and two variably controllable by the control means 2 delay circuits 9a, 9b available, wherein the first delay circuit 9a between the local oscillator 8 and a light detector 10 is disposed and with respect to the transmission pulse 7 delayed sampling pulses 11 produced for scanning the measurement pulse 4 and the reference pulse. 6 The second delay circuit 9b is disposed between the local oscillator 8 and a light transmitter 12 in the form of a laser diode for transmission of the transmit pulse. 7 The controllable delay circuits 9a, 9b in the form of digital, fully integrated delay blocks each comprise a programmable frequency divider 21 before the outputs to which each pulse shaper 13 downstream. In addition, a control means 2 connected to the phase detector 14 is present, at whose two inputs of the transmission pulses and the sampling pulses 7 eleventh The light detector 10 is designed as an avalanche photodiode, the reverse bias U_APD is superimposed by the power supplied by the local oscillator 8 sampling pulse train, wherein the amplification factor of the avalanche photodiode in the blanking intervals of the sampling pulse is substantially lower than during the presence of the sampling pulses 11. Furthermore, the light detector 10 is connected to a low-pass 15 which is connected to an amplifier 16 which is connected to an analog-to-digital converter 17 which is connected to the control means the second Thus, the resulting sensing result when scanning is first low-pass filtered, then amplified in the form of an analog DC signal is then sampled by the analog to digital converter 17 and finally supplied to the digital control means the second

p0023After <figref idrefs="f0002">FIG. 2</figref> , the algorithm of the control means 2 (<figref idrefs="f0001">Fig.1</figref>) Executed measurement process a calculation step 18 to uniquely calculate the distance D. These multiple runtime determination steps 19 performed f with different pulse repetition frequencies within the calculation step 18, each determining an associated time difference [tau] between the measurement pulse 4 and the reference pulse 6, but which taken individually is not necessary to a unique distance D can close. This is, however, clearly calculated in the calculation step 18 as a solution of a linear system of equations from all pulse repetition frequencies f and time differences [tau]. Within this term determination steps 19 several scanning steps 20 are carried out, which is repeated several times by the light detector 10 (<figref idrefs="f0001">Fig.1</figref>) Received and a pulse repetition rate f periodic measurement pulses 4 (or in temporally successive scanning the reference pulses 5) directly on the light detector 10 (<figref idrefs="f0001">Fig.1</figref>) By sampling pulses 11 exactly this pulse repetition frequency f scan and the scan result from the control means 2 (<figref idrefs="f0001">Fig.1</figref>) Collect, where the control means 2 (<figref idrefs="f0001">Fig.1</figref>) By means of the delay circuits 9a, 9b (<figref idrefs="f0001">Fig.1</figref>) The sampling pulses 11 are delayed variably controlled with respect to the transmitter pulses 7, and in the overall duration determining step 19, the time difference [tau] between the measurement pulses 4 and the reference pulses 6 from exactly correspond to the time delays will be calculated, the successful sampling events are associated.