DE19540590A1 - Level sensor for rotary laser - Google Patents

Abstract

The laser level sensor detects and provides a numerical display of height variation relative to a reference horizontal generated by a rotating laser beam. The sensor determines the height difference, between the centre of the sensor or a user defined null point, and the reference horizontal, via time measurement. Preferably, incident laser light is successively conveyed to at least two (1-3) linear optical receivers and is then fed to an analyser stage after converting it to electric signals. At least one (2) of these receivers is arranged at a constant angle to the others (1,3). The receivers are not position sensitive and serve only to generate electronic pulses with which cycle time measurements of the beam between the receivers are started and stopped. The measurements are used to determine and electronically display the incident light of the beam.

Description

In measurement technology there are two different types of receivers known for rotating lasers that work according to the following principles:

In the first genus, an incident is used to determine the center Laser light spot a symmetrical arrangement of two groups of Photo receivers used. Here is by difference or comparison method recognized an off-center position of the spot center and z. B. with Illuminated displays symbolize (Bertold Witte and Hubert Schmidt: Surveyor and basics of statistics for the building industry, publishing house Konrad Wittwer, 2nd edition, Stuttgart 1991, page 580), (Hennecke / Müller / Werner: Handbuch Engineering Survey Volume 1, publisher Wichmann, 2nd edition, Heidelberg 1994, pages 119f and 170f).

The receiver unit is now either manually (the entire sensor) or motorized (DE 38 33 153 A1) with a fixed outer housing as far as shifted up or down until the laser spot is centered on an imaginary one Dividing line (zero line) between the two groups of photo receivers. At the motorized version can also be adjusted be specified numerically (Geo-Feinmechanik GmbH Mülheim / Ruhr).

In the case of sensors of the second type, a row-like arrangement of individual ones is used Photo receiver perpendicular to the reference horizon to determine the center of the incident laser light spot used. (Spektra Physics, Nestle & Fischer, Dornstetten).

The sensors of the first kind have the following disadvantages:

With the sensors that have to be moved to the "zero line" by hand, can only transfer a height, but not a direct, quantitative measurement the height difference between the center of the sensor and the reference horizon will. They also have a small measuring range. The sensors with Motorized adjustment of the receiving unit are due to the need mechanical drive elements (motor / spindle / rack etc.) in their Manufacturing complex and susceptible to wear in continuous operation.  

For the production of sensors of the second type, this is for everyone Photo receivers (photodiode or transistor) require a signal shaping stage Lich to be able to control an evaluation. Furthermore, their dissolution limited by the size of the photosensitive surface of each Photo receiver.

The invention specified in claim 1 is based on the problem to develop a leveling sensor for rotating lasers in which none movable components are required, which has a large measuring range and a numerical display and a data transmission of the Height difference value between the center of the sensor or a user-defined one Zero point and the reference horizon of the laser with a high resolution and Accuracy allowed.

This problem is solved by those listed in claims 1 and 2 Features solved by deriving the altitude values from time measurements and linear optical receiving units are used for this.

The advantages achieved with the invention are in particular that none moving components are required and therefore the level sensor in the Continuous operation is not susceptible to wear. This is especially true with continuous Height monitors, e.g. B. on buildings or in the civil engineering area of Meaning where you could use a larger number of these sensors, about the influence of excavation, pressing, groundwater subsidence conditions, mining etc. on the daily surface.

Fig. 1 shows the principle of operation of the invention using the example of an arrangement of three linear optical receiving units.

The unit ( 2 ) is arranged at a constant angle to the other two receiving units ( 1 , 3 ).

The three linear optical receiving units ( 1 , 2 , 3 ) can each consist of:

• - Lined up, commercially available optoelectronic sensors (Photo diodes, photo transistors) in parallel, or  
• - a bundle of optically conductive glass or plastic fibers, that on the reception side a linear cross-section and on the exit side has a round cross section, where the received laser radiation from an optoelectronic sensor is registered, or
• - A specially machined rod made of optically conductive material appropriate length that is able to share the right angle absorbing incident laser radiation and axially parallel to one of the two rod ends where the received laser radiation is registered by an optoelectronic sensor.

All of the above Designs of linear optical receiving units are not sensitive to position. The laser light, which is at any height line-shaped optical receiver unit, causes only the generation of one electrical pulse, which is used as a start or stop signal.

By rotating the laser beam in a clockwise direction, the three linear optical receiving units are hit at points A, B and C ( FIG. 1). The two times are measured which are proportional to the distances z1 and z0. The desired height h, which specifies the distance between the sensor center or the user-defined zero point and the reference horizon of the rotating laser, is based on the formula

with Hg: dimension between the two imaginary intersections S in ( Fig. 1)
and Hm: dimension calculated between the lower intersection S and the sensor center or the user-defined zero point.

The arrangement shown in Fig. 1 three linear optical receiving units th has the advantage that changes in the rotational speed of the rotary laser and systematic measurement errors in the determination of z0 and z1 have no influence on the measurement result h, because with the help of the value z0, the unchangeable Distance between the two outer, vertically arranged receivers is represented, the relevant quotient z1 / z0 is normalized.

However, if you have sufficient stability of the Laser Rotationsge speed as well as the timing can also build a Leveling sensor for rotating lasers with only two linear optical Receiving units possible, in which the two receiving units in one defined angles to each other.

Fig. 2 shows a front view of an embodiment of a level sensor for rotating lasers. The linear optical receiving units ( 2 , 3 , 4 ) mounted behind a filter disc in the housing ( 1 ) each consist of commercially available photodiodes lined up in parallel. The distance between the light-sensitive surfaces of the photodiodes is approximately 2 mm, so that a sharply focused laser beam is also detected by at least one photodiode. Embodiments with a larger distance between the photodiodes or a reduced number are conceivable if rotating lasers with a larger beam diameter are used.

The button ( 5 ) is used to switch the level sensor on / off. By pressing the "FUNCTION" button ( 6 ) you can choose the unit of measurement used and define a new zero point. The respective selection is activated with the "SET" button ( 7 ). The two-color light-emitting diode ( 8 ) serves to visualize the operating state of the level sensor. If it lights up red, there is a fault; if it lights up green, a normal measuring cycle is running. The measured value h is displayed in the selected unit of measure on the LCD display ( 9 ) and passed to the data output ( 11 ), from where the value can be read in by a personal computer or a data collector or sent to another leveling sensor of the same type can operate a fieldbus system that connects several leveling sensors. The data input ( 10 ) is provided for this purpose.

The block diagram ( Fig. 3) serves to further explain the mode of operation:

The electrical impulses generated by the optoelectronic sensors are converted by three signal adjustment stages into TTL-compatible start / stop signals. As soon as the start pulse A ( FIG. 1) appears, which triggers an interrupt request in the microcontroller, the counter readings Z0 and Z1 are decremented in the counter with each clock of the clock generator, starting in each case with the start value 65535. The counting process Z1 is stopped by the laser beam striking the obliquely arranged receiving unit at point B ( FIG. 1); the impact of the beam on point C ( FIG. 1) stops the counting process Z0 and initiates the evaluation by the microcontroller system:

First, the meter readings Z0 and Z1 of the meter are read in and the Differences z0 = 65535-Z0 and z1 = 65535-Z1 are formed. After a Plausibility check of the values z0 and z1 is the value h after the above. formula calculated and output on the LCD display and to the data output headed. The two-color LED that is activated in the "green" operating mode indicates a correct measurement. After the issue of Value h is a measurement completed. The microcontroller system sets then the counter back and initiates the next measurement.

The following circumstances can occur during the plausibility check or through internal In The microcontroller requests the invalidity or impossibility signal a measurement:

• - Case A: The value z1 is greater than the value z0
• - Case B: No signal is received within a defined time window
• - Case C: The counter reading Z0 or the counter reading Z1 reaches zero.

Case A occurs when the rotation of the rotating laser is not clockwise he follows. The text "Wrong direction of rotation!" Will then appear in the LCD display. out give. In case B, either an obstacle has the level sensor completely shadowed or the rotating laser does not work. The LCD display shows then the text "obstacle / laser failed!" spent. In case C is the Distance to the rotating laser and / or the rotating speed too low or the connection to the laser was briefly interrupted. In the LCD The text "too slow - too close / interruption!" spent. In all of the above Cases is activated by switching on the two-color LED in the Be drive mode "red" signals a fault and the respective message texts output the data output.  

By pressing the "FUNCTION" button, the current measuring cycle becomes interrupted and the possibility to choose the unit used ([mm] or [inch] for the value h) and for the definition of a new zero point given. The respective selection is activated and activated with the "SET" button Returns to the measuring cycle.

Claims (2)

1. Leveling sensor for rotating lasers for the detection and numerical display of changes in height compared to a reference horizon generated by a rotating laser beam, characterized in that the height difference between the sensor center or a user-defined zero point and the reference horizon of the laser is determined by time measurements. 2. Leveling sensor for rotating laser according to claim 1, characterized characterized in that incident laser light on one after the other conducted at least two linear optical receiving units and after transformation as electrical signals of an evaluation stage is supplied, at least one of these receiving units in at a constant angle oblique to the other Receiving unit (s) is arranged.