WO2001007863A1

WO2001007863A1 - Measuring system for determining a distance and a lateral deviation

Info

Publication number: WO2001007863A1
Application number: PCT/EP2000/005112
Authority: WO
Inventors: Joachim Tiedecke; Norbert Amann
Original assignee: Idm Gmbh Infrarot Sensoren
Priority date: 1999-07-22
Filing date: 2000-06-05
Publication date: 2001-02-01
Also published as: AU5401600A; DE19933877A1

Abstract

The invention relates to a measuring device designed for optically measuring the distance and lateral deviation of an object. The device comprises a transmitter (1) composed of a light source (2) for transmitting a measuring beam and an optical system (5) for collimating said measuring beam about a measuring axis (4), a reflector (6, 6', 23) associated with the object, and a receiver (2), whereby the light source (2) is provided with tracking means (7, 8, 9) for scanning the light beam in at least one lateral direction which is transversal to the measuring beam.

Description

Measuring system for recording the distance and the lateral placement

The present invention relates to a measuring device with the features of the preamble of claim 1 and a method for determining the distance and the lateral placement of an object.

Such devices and methods are known from practice. For example, generic measuring devices are used to determine the position of gantry cranes on a crane runway. This measurement serves in particular to influence the drive control in two gantry cranes so that the cranes cannot collide with one another. In addition, the control of the crane is intervened in such a way that it is gently braked at the end of its career and comes to a standstill. Devices for measuring distance are known which measure the distance from the measuring device to the object on the basis of a transit time of a signal from the measuring device to the measuring object and back. The measurement object is usually equipped with a reflector for accurate measurement of the distance. Furthermore, measuring systems are known which detect the lateral placement of an object in relation to a measuring axis. A sensor has a measuring beam divided into two beams. The energy reflected by the reflector is recorded and measured separately in the two measuring beam halves. The ratio of the energies m to the two measured, reflected measuring beams is proportional to the lateral displacement of the detector from the measuring axis.

For long distances, such as those occurring in crane runways with lengths of 250 m and more, the measuring system should sit on the moving crane if possible, so that the control signal for the drive motors is immediately available and does not have to be transferred from the fixed crane runway to the moving crane. For this purpose, the reflector must be firmly attached at the end of the crane runway. However, like almost all moving systems, gantry cranes tend to yaw around the vertical axis, which leads to the measuring axis moving on the reflector. This problem is either solved by designing the measuring beam so large that the reflector is in the area of the measuring beam even with maximum misalignment, or by designing the reflector so large that the measuring beam always hits the reflector reliably. Both solutions lead to beam cross-sections or reflector sizes in the range of 1 to 2 m with an assumed length of a crane runway of 250 m and the usual yaw angles. It is problematic that a greatly expanded measuring beam reflects only a relatively small amount of energy, which can lead to inaccuracies in the measuring process on the receiving side, and that, on the other hand, a reflector of the size described is very unwieldy.

It is therefore an object of the present invention to provide a measuring system and a measuring method which, even when mounted on a movable platform with a small reflector, allows a measuring beam with a small opening angle, the method nevertheless being able to provide results which are equivalent or superior to the prior art. This object is achieved by a device with the features of claim 1 and by a method with the features of claim 10.

Because it is provided that the transmitting unit has tracking means for pivoting the measuring beam in at least one lateral direction transverse to the measuring beam, a light beam with a relatively small cross section can be directed onto an equally small reflector and upon rotation of the base of the measuring device by one certain greediness can be adjusted. On the other hand, the measuring axis can also be tracked in the event of a lateral migration of the reflector and a stationary measuring device. The reflector can be kept small without fear of significant losses in signal strength, which would lead to limited accuracy. In addition, the lateral placement of the size can be easily determined. If the optical system has a variable focal length and means for changing the focal length, the beam can be colimized at any distance can be varied so that the reflector is always illuminated over its entire surface, without a significant part of the measuring beam passing the reflector. This measure also leads to good accuracy, since a good measurement signal can be achieved with compact dimensions.

A simple mechanical solution results if the light source can be moved in the lateral direction with respect to the optical system and / or the optical system can be moved in the lateral direction with respect to the light source. Provision can also be made for the light source and the optical system to be arranged so as to be pivotable about a common axis. It is generally easy to reach and yet sufficient if the tracking means are set up to cover a swivel range of 1 ° to 5 °. The tracking means are advantageously driven by electromechanical actuators, in particular by piezoelectric transducers or electric servomotors. Depending on the application, the tracking agent can be selected appropriately. If the light source emits an at least two-part steel, the partial beams of which are arranged symmetrically to the measuring axis, the beams can simply be discriminated spatially, temporally, according to their wavelength or according to their polarization. It can also be provided that the receiver receives light from a plurality of spatial regions which are arranged essentially symmetrically to the measuring axis. The solid angle ranges are then selected so that they are aligned essentially symmetrically on the reflector by the tracking means. The receiver can advantageously have a two-quadrant photodiode or a four-quadrant photodiode. Hereby are a measurement of the lateral offset in one direction and, on the other hand, a measurement in two spatial directions are possible.

Because the following steps are provided in the method according to the invention:

- emitting the measuring beam from the light source to the reflector;

- Registering the reflected portion in the receiver, preferably in a certain distance window;

- Determining the position of the measuring axis of the measuring beam on the reflector;

- Swiveling the measuring axis through an angle until an approximate or perfect match of the position of the measuring axis with the center of the reflector is achieved;

- Determine the distance of the object

- Determining the lateral placement of the object from the distance and the angle;

it is possible to align the measuring beam with the reflector, which enables a good signal-to-noise ratio and, moreover, information about the lateral placement can be achieved. It is advantageous if the focal length of the optical system is additionally varied such that the cross section of the measuring beam in the region of the reflector corresponds approximately to the area of the reflector, regardless of the distance. This can be achieved in a simple manner if the focal length is varied as a function of the distance. The lateral placement can be m particularly effective from a control signal for pivoting of the measuring beam can be determined. Overall, it is advantageous for continuous measurements if the method steps are repeated several times, in particular with a high frequency.

An exemplary embodiment of the present invention is described below with reference to the drawing.

Show it:

Figure 1: An inventive device with several options for determining the distance and the lateral placement of a reflector in a schematic representation; such as

Figure 2 is a schematic plan view of a gantry crane with an inventive device for determining the distance from an end point of the track.

FIG. 1 shows a measuring device according to the invention in a schematic plan view, several embodiments being combined in one illustration.

A transmitting and receiving unit 1 comprises a light source 2 for emitting a light beam 3 m in the direction of a measuring axis 4 and a receiver 2 'for receiving reflected light along the measuring axis 4. The light beam 3 passes through an optical system designated 5 overall and is applied to one Reflector 6, 6 ^λ collimates. In this embodiment, the optical system 5 has a total of three lenses, the overall focal length of which can be varied, so that when the reflector 6 is relatively close, the light beam 3 is one Obtaining opening cti to illuminate the reflector 6 approximately m over its entire surface. At a large distance, which is symbolized by the reflector 6 ^λ , the light beam receives an opening angle α ₂ which is smaller than the angle oti and illuminates the reflector 6 ^{λ of} the greater distance.

The light reflected by the reflectors 6, 6 ^λ is reflected by the same optical system 5 m, the transmitter and receiver unit. There it falls on the receiver 2. The signal transit time is initially used in a manner known per se for determining the distance. In this embodiment of the invention, the sensor means 2 is set up to detect the position of the generated image on its sensitive surface. For example, two or four quadrant diodes are suitable for this. Suitable diodes are available, for example, under the type designation S3060-02 from the manufacturer Hamamatsu (Japan).

The optical axes of the systems 5 and 5, which are closely adjacent spatially within the transmitting and receiving unit, practically coincide at real distances of a few meters and form the measuring axis 4.

The emitted and / or the reflected measuring beam is divided into two or more partial beams, the backscattered intensity of which is measured in each case. When the measuring beam 4 ^λ migrates with its axis 4 from the center of the reflector 6, the ratio of the intensities changes in proportion to the lateral placement. At the same time, the total intensity, which is available as a measurement signal, decreases when the measurement beam 4 emigrates from the reflector 6.6 ^λ , so that the Accuracy of measurement suffers. In the device according to the invention, e emigration of the reflector 6 ^{Λ in} a direction denoted by I is compensated for by pivoting the measuring axis 4. Various options can be implemented in the transmitter and receiver unit for this purpose. A first embodiment consists of the displacement of the optical system 5 by an actuator 7 in a direction II transverse to the measuring axis 4. The second possibility provides an actuator 7 for displacing the light source 2 and the sensor means in a direction III under the influence of an actuator 8 , Finally, in a third embodiment, the entire transmitting and receiving unit 1 can be rotated about a vertical axis 10 via an actuator 9, which is symbolized by the directional arrows IV.

From the ratio of the intensities of the partial beams, first, the lateral offset of the measurement axis 4 on the reflector 6, measured ^λ 6 and recovered em control signal therefrom, the one or more of the actuators 7, applied 8 or 9 with a control signal, such that the lateral Storage of the measuring beam 4 on the reflector 6, 6 ^{λ is} regulated towards zero. From the control signal with which the actuators 7, 8, 9 are applied, a measured value is obtained via the pivoting of the measuring axis 4. From this value and the already determined distance of the reflector 6, 6 ^λ from the transmitting and receiving unit 1, the lateral placement can then be calculated in a simple manner, for example in length units.

The focal length of the optical system 5, 5 can be changed by varying the distance V as in a zoom lens known per se. For this purpose, an actuator (not shown in more detail) with a control or control signal applied. The control is carried out in such a way that the measuring beam illuminates the reflector 6, 6 over all areas. The regulation can take place via a known, optionally calibrated dependency between the focal length of the optical system 5, 5 'and the distance from the reflector 6, 6 ^λ , so that a suitable angle α i or α _{2 is} set inevitably. However, a regulation can also be provided which initially selects a larger angle oti than would actually be required and then reduces the angle by increasing the focal length. Here, the scattered intensity increases, since a larger part of the measuring beam is reflected by the reflector 6, 6. As soon as the reflector reflects the entire measuring beam, a maximum value is reached which does not increase any further. This maximum value is then maintained for the respective distance. This achieves the maximum signal intensity and at the same time the best possible measurement accuracy both for the lateral placement and for the distance.

In practice it is sufficient if one of the adjustment possibilities (direction II by means of actuator 7, direction III by means of actuator 8 or direction of rotation IV by means of actuator 9) is realized. The angles required in practice by which the measuring axis 4 can be pivoted are usually a few degrees.

The variable focal length (V), which is described in this preferred embodiment, can also be dispensed with insofar as the angle differences oti - α _{2 are} small. An application example of the present invention is shown in FIG. 2. FIG. 2 shows a schematic top view of the use of a device according to the invention for controlling a gantry crane 20 along a track 21 that ends in the region of a wall 22. A reflector 23 is attached to the wall 22 and corresponds to the reflectors 6, 6 ^λ from FIG. 1. It is a retroreflector with dimensions of approximately 50 cm × 50 cm, for example of the Scotchlite type from the manufacturer 3M (USA). The transmitting and receiving unit 1 is fixedly mounted on the portal crane 20 and emits a measuring beam 24 m in the direction of the reflector 23. The distance of the reflector 23 from the transmitting and receiving unit 1 is determined from the transit time of the signal. If the gantry crane 20 is now moved in the direction of its running track 21 m, a yaw movement occurs in practice about a vertical axis 25 of the gantry crane 20, since the drives assigned to the two running tracks 21 cannot be driven absolutely synchronously. The magnitude of this yaw movement can be approximately 1 °. The measuring beam 24 is pivoted in the lateral direction by this angle, so that it migrates from the reflector 23. The measuring beam 24 is then regulated with its measuring axis by one of the three possible acaching devices (actuators 7, 8, 9) back to the center of the reflector 23. The control signal is a measure of the yaw curve of the gantry crane 20. It can be seen that with a track length of 250 m and a yaw curve of only ± 0.25 °, the area of the wall 22 covered by the measuring beam 4 is over 2 m. A transmitting and receiving device equipped without tracking the measuring beam 24 had to have a reflector in 01/07863 _] _] _ _ PCT / EP00 / 05112

with a width of over 2 m. In practice, this is undesirable.

The present invention thus enables the use of small reflectors 23 that are easy to assemble and require little space. Due to its tracking, the measuring beam always falling centrally on the reflector enables a particularly precise distance measurement due to its high reflected intensity. At the same time, a measure for the yaw angle of the gantry crane 20 is obtained from the tracking signal, which can optionally be used for the synchronous control of the drive motors of the gantry crane.

Claims

P a t e n t a n s r u c h e

1. Measuring device for the optical detection of the distance and the lateral placement of an object, with a transmitting unit (1) which has a light source (2) for emitting a measuring beam and an optical system

(5) for collimating the measuring beam around a measuring axis

(4), and with an object assigned reflector (6, 6 ^' , 23) and with a receiver (2'), since you rchgek characterized that the transmitter unit (1) tracking means (7,8,9) for pivoting the Measuring beam (4) in at least one lateral direction transverse to the measuring beam (4).

2. Measuring device according to claim 1, d a du r c h g e k e n n z e i c h n e t that the optical system

(5) has a variable focal length and means for changing the focal length.

3. Measuring device according to claim 1 or 2, since you rchgek characterized that the light source (2) relative to the optical system (5) m of the lateral direction (III) is movable and / or that the optical system (5) relative to the light source (2nd ) m can be moved in the lateral direction (II).

4. Measuring device according to claim 1 or 2, since you r c h ge k e n n z e i c h n e t that the light source (2) and the optical system (5) about a common axis

(10) are arranged pivotably.

5. Measuring device according to one of the preceding claims, since you r ch ge k e n n z e i ch n e t that the tracking means (7,8,9) are set up to cover a swivel range of 1 ° to 5 °.

6. Measuring device according to one of the preceding claims, since you r c h ge k e n n z e i c h n e t that the tracking means (7,8,9) are driven by electromechanical actuators, in particular piezoelectric transducers or electric servomotors.

7. Measuring device according to one of the preceding claims, since you r ch ge k e n n z e i ch n e t that the light source (2) emits an at least two-part beam, the partial beams of which are arranged symmetrically to the measuring axis.

8. Measuring device according to one of the preceding claims, since you r ch ge k e n n z e i ch n e t that the receiver (2 ') receives light from several solid angle ranges, which are arranged substantially symmetrically to the measuring axis (4).

9. Measuring device according to one of the preceding claims, since you r ch ge mark that the receiver (2) has a two-quadrant photodiode or a four-quadrant photodiode.

0. Method for determining the distance and the lateral placement of an object, by means of a device with a transmitter unit, which comprises a light source for emitting a measuring beam and an optical system for collimating the measuring beam about a measuring axis, and with a reflector assigned to the object and with a recipient, characterized by the following steps:

- emitting the measuring beam from the light source to the reflector;

- registering the reflected portion in the receiver;

- Determine the distance of the object

- Determine the lateral placement of the object from the distance and the angle.

11. The method according to claim 10, since you are characterized that additional provision is made to vary the focal length of the optical system so that the cross section of the measuring beam in the region of the reflector corresponds approximately to the area of the reflector.

12. The method of claim 11, since du r ch ge ke nn zeic hn et that the focal length is varied depending on the distance.

13. The method according to any one of the preceding claims, since you r c h ge k e nn z e i chn e t that the lateral storage is determined from a control signal for pivoting the measuring beam.

14. The method according to any one of the preceding claims, since you r c h ge k e n n z e i ch n e t that

Repeat procedural steps several times.