DE19504126A1 - Contactless measurement of three=dimensional objects using optical triangulation - Google Patents

Abstract

The surface of the object reflects a focussed beam from a light source and the remission is detected by light detectors. The light source and detectors are arranged in a sensing head which can be moved linearly and pivoted. The position of the reflected light is determined on a CCD row used as a detector to determine the distance of the detected point on the object surface. The object is rotated to enable peripheral, annular, horizontal scanning in the z direction. The resulting data are stored and used for three-dimensional reconstruction of the object with a data processing unit. The annular scan is repeated with a predefined z-scan step using different angular positions of the sensing head, e.g. for detecting undercuts, covered points or x-parallel planes or surfaces.

Description

The invention relates to an apparatus and a method for non-contact measurement of three-dimensional objects on the Basis of optical triangulation according to the generic term of Claims 1 and 9 respectively.

Method for the contactless measurement of the outer contours of three-dimensional objects by means of electromagnetic radiation tion based on optical triangulation are known. The object is located on a turntable and is by means of a scanning unit that is relative to the turntable  is movable in the x and z directions and a radiation source and contains radiation detectors. At suchi devices from the scanner The measuring beam reflected and remitted on the object with regard to the Point of impact on one arranged in the scanning device th sensor examined, the sensor output signal with an evaluation unit is processed with computer support, to provide appropriate information about the object surfaces distance, x, y and z position of the scanning unit and the Detect the rotational position of the turntable in order to turn it to provide three-dimensional, digital data.

Such data are then stored in order to 3D image processing systems, e.g. B. to control a numeric Machine tool to be available.

The measurement of three-dimensional objects using optoelectro sensors and based on triangulation Accurate data acquisition, which is possible faster than when this was realized with mechanical scanning devices can be.

In the device known from DE 39 10 855 C2 for The constructive should measure three-dimensional objects Effort, especially for moving the scanning unit in X and Z direction can be simplified. According to the solution there becomes a commercial EDP plotter as an X and Z slide used for the scanning unit, which is on an L-shaped Base frame is mounted. The horizontal leg of the L-shaped Base frame is used to fasten the turntable, the aforementioned EDP plotter on the vertical bar kel of the base frame is arranged.

A problem arises when using the one shown there Device objects to be measured, the rear have cuts or hidden areas. In this  The measuring unit must also trap in the Y direction be movable. Such, in two planes perpendicular to mutually displaceable, on the one hand, increases the mechanically constructive effort and leads to the other an instability and mechanical vibrations of the whole Unit of measurement. Furthermore, it is extremely difficult Position change on two levels as quickly as possible with high dynamics changes, it should be borne in mind that inaccurate positioning of the scanning unit with the Senso Ren or the radiation source a significant deterioration measurement accuracy.

It is therefore an object of the invention, a device and a Method for non-contact measurement of three-dimensional objects objects based on optical triangulation to indicate which allow an object with high precision even then measured if this object covered undercuts Places, blind holes or the like.

The object of the invention is achieved with a counter stood according to the features of claims 1 and 9, wherein the subclaims at least useful configurations and Training includes.

The basic idea of the invention is to make a scan form head, which in vertical, d. H. in the z direction is linearly movable and also a drive unit has a predetermined pivoting, tilting and / or rotating the scanning head on a given one a z position, i.e. H. at a fixed point.

According to a further idea of the invention, the movement takes place of the turntable, which is to measure the inclusion of the serves the object, quasi-continuously, which means un desired vibrations of the object or the entire device  device with the disadvantage of low measurement accuracy, as is the case with stepwise rotary drive is avoided.

The three-dimensional measurement then takes place in that the object located on the turntable or turntable a ring-like circumference, not necessarily gone sequential order, is sampled point by point. To Every turn of the turntable the scanning head moves in the z direction transported by a predetermined step. Then the next ring and is scanned the corresponding data transmission. The above procedure Repeatedly is repeated until the entire object is scanned circumferentially. The to a subordinate data Describe information transmitted to the processing device accordingly points on the surface of the object as X-, Y-, Z coordinates.

The scan described above is at least in a predetermined angular position of the scanning head leads. It has been found that very uneven objects a multiple scan, quasi to form a Scanning point cloud, in different angular positions is appropriate. With the help of this multiple scanning a special scanning window formed, the in this Fen most received variety of information in the data processing processing unit for a clear statement about the confi guration or surface design of the object to the this point is assembled.

Due to the possibility of swiveling the viewing direction of the Readhead around the vertical axis by a certain amount Selectable angles can have different viewing directions the object can be set. This can be advantageous hidden parts of the surface by measurements with Attacks are recognized. Otherwise you can't do that visible areas of the object, especially in the case of multiple  contiguous surfaces, e.g. B. surfaces with Through holes, be scanned with sufficient accuracy. By an adjustment of the viewing direction of the scanning head Tilt the same by essentially 90 ° around the roll axis of the Direction of observation and swiveling the measuring head gaze direction in the inclination axis by a preselectable angle badly avoidable surface pieces of the object, such as. B. Axis close to the axis or largely horizontal or horizontal surface areas are recorded.

By multiple existing receiver modules, d. H. Beam tion detectors and corresponding optics can be higher Signal truth can be achieved. This serves the verb improvement of signal security in the case of remission problems corresponding logical test algorithms. Ultimately it will hereby the horizontal position accuracy by geometrical Switching off the symmetry error improved and the Abso bleeding errors reduced.

Another essential basic idea of the invention exists in using a dynamic control of light output Detected radiation source, e.g. B. a laser diode, whereby the probability of interpretation of the remitted Light signal on the radiation detectors and thus the measurement accuracy can be increased. Through a simple, tax bare extension of the integration time as the radiation end Detectors used CCD lines or increased lasers light intensity can also be very distant, very angular unfavorable and / or weakly reflecting objects safely be measured.

Obtaining depth information from the Ge obtained The total signal of the CCD line signal occurs once by measuring both signal peak edges and arithmetic averaging or on the other hand with an unfolding or partial unfolding, e.g. B. through appropriate analog signal processing, in which  first high frequencies are filtered out, differentiated, smoothed, differentiated again and then from the smoothed subtracted the weighted second derivative is hated. Alternatively, digital unfolding or De fuzzyfication done.

The method according to the invention and the associated device are now based on an embodiment and Figures are explained in more detail.

Here show:

Fig. 1a, b basic representations of the optical triangulation tion process with the aim of clarifying the principle of action of the scanning head and

Fig. 2 shows the basic structure of the device with the indicated possibilities of pivoting and tilting the scanning head.

With FIGS. 1a, b first the measuring geometry of the scanning head and the resulting unrealized optical triangulation will be briefly explained.

Two CCD lines 1 are arranged in a predetermined angular position, essentially symmetrical to the beam path of a laser 2 serving as a radiation source. A corresponding lens 3 is assigned to each CCD line 1 . a is a measuring point of the object to be measured and the line pixel number na represents the measuring standard of the measuring distance a, which is obtained by means of the CCD lines 1 .

The bundled light emitted by laser 2 is reflected by the surface of the object to be scanned. The remission portion is detected within the measuring range by the optics 3 and is evaluated as a measured variable na from the respective CCD lines 1 . This position determined on the respective CCD line 1 is used as a measure for determining the distance of the scanned point on the surface of the three-dimensional body.

Since the receiver lens image field still has a residual curvature, the focus will only be at 2 points on the flat CCD line ideally sharp. In the triangulation calculation the main lens plane distances, the beam offsets by the CCD line window and the band filter as well as the measured CCD line averages and / or data in the form of a scannob project-related target calibration taken into account.

The object location data triplet calculation is done under Berück view of the measuring head / object axis of rotation distance, the obj tiv rotation angle position, the measuring distance, the measuring head swivel kels, the measuring head tilt angle and the increase of the measurement over the turntable level at the measuring head.

In one embodiment of the invention, the CCD lines 1 and / or the objectives 3 are movable. The radiation of the laser 2 is dynamically focused with an automatic focusing, not shown, to be explained later, in order to increase the measuring accuracy in objects with different diameters.

Due to the multiple existing receiver modules or CCD line 1 with the associated lenses 3 , the error probability is reduced by switching off errors caused by the measuring principle and problems with different remitting surfaces or surface parts of the object are switched off.

Using special steps, the data is opened Relevance checked.

Ideally, the measured value is averaged from both channels.  

If a measuring channel fails due to a missing signal, only the other channel used for the acquisition of measured values. That applies u. a. also for measuring signal amplitudes that are too low, for measuring signals au outside the measuring range and for double signals.

The identified causes of the error will also be eliminated value calculator reported.

Depending on the object surface properties, the lines sensitivity can be selected.

To increase the resolving power, the physical Number of photo elements (number of pixels) of the CCD lines on electri factually doubled.

Data records generated per object revolution are interposed saves. By changing the memory after every full ob Project rotation and alternate transmission is a seamless process free, i.e. 36 ° comprehensive image of the object surface also possible at the highest sampling rate.

The CCD line pixel number data is in object surfaces converted pixel data and can by their ordered An case in a special extremely space-saving data format.

It is within the meaning of the invention to measure accuracy Increase measured value accumulation and averaging and the To minimize the effects of noise.

The kinematics of scanner and adjustment devices are chosen so that 180 ° panning and / or location exchange last rer a favorable subtraction of the errors in Meßent distance, axis of rotation transverse and longitudinal deviation as well as beam egg enable and perpendicularity errors.

Remaining but measured residual errors in the scanning kinematics and the guideway straightness and flatness or leadership  misalignments can be added or subtracted from ke gel frustum-shaped correction bodies at the object location triplet calculation are taken into account.

For quasi-dynamic or time-resolved measurements by continuous repetition measurements with extremely fast measured value or data flow, individual points, rings, spiral tracks or vertical lines can also be used as quasi-space-space measured value windows for the analysis of the time behavior, e.g. B. for the egg gene vibration behavior, be selected. The CCD lines 1 can be adjusted in three directions of translation and rotation (not shown). The lines can be adjusted so that several lines show approximately the same CCD single photo element numbers, and that the signal dynamics within a line are largely the same under the same external conditions.

The measuring accuracy can be further increased in that a specially shaped, combined perforated and ring diaphragm or a corresponding aperture set is available and designed in this way is that the superposition of the diffraction phenomena largely smoothest envelope of the light spot structure on the Object results.

The optics used for the laser 3 allow the formation of an illumination surface on the object with a diameter of less than or equal to 0.2 mm. The support for the lenses 3 is based on the arrangement of the CCD lines 1 separately and can be pivoted in a range of 5 to 20 ° for corresponding angles with respect to the light wave axis. Instead of the laser used, alternatively a high-pressure xenon lamp with a corresponding collimator can be used to adjust the beam waist and to form a quasi-point light source.

The laser 2 , the collimator and the collimator drive are designed as a uniform optical focusing unit. The movable collimator elements required for focusing are completely suspended in the collimator drive.

The actual collimator drive consists of the An drive unit and the collimator suspension together, which essentially from a spring generating a counterforce unity exists. The moving parts of the collimator drive bes and the collimator suspension are lightweight preferably using plastic laminates leads. Using the special collimator drive, the Setting the focus point on the object by the package mator and with a dynamic down to the kilohertzbe done richly.

The drive unit of the collimator is a linear drive with high acceleration due to low mass at high Adjustment speeds. The drive itself sits directly on the optical axis, creating a direct power transfer and minimizing secondary path errors is achieved. The drive is still a magnetic plunger trained system, the plunger a roughly li has a linear characteristic. The drive mentioned above is operated under preload. This allows after me basic setting of the focusing unit, this elec tric fine adjustment and optimal areas if necessary the interaction of the preload characteristic and the characteristic line of the actual drive.

The collimator drive is controlled electrically in such a way that the deflection current is PID-like from an acceleration current pulse, the actual deflection current and a short Ab brake current pulse, superimposed by a constantly applied Basic adjustment current. This can be extremely can be adjusted and focused quickly and easily.  

Determining the amount of electricity for magnetic drive control follows an optical distance by evaluating the measurement signal tension meter and look-up tables and subsequent descriptions calculation using a single-chip microcomputer. With attention of the focal point curve can provide the current signal adaptive or based on experience to be provided in a quasi-fuzzy logic way. Hereby is a particularly fast, highly dynamic focusing possible.

Fig. 2 is illustrative of the apparatus for three-dimensional objects and Vermes sen shows a U-shaped base frame 4 substantially. A turntable 5 forms one leg. The drive for the turntable 5 is also located in the horizontal, foot-shaped part 4 . The design of the drives as micro-stepper drives with special acceleration and deceleration curves ensures safe, low-vibration operation.

The distance between the measuring head and object turntable rotation axis can be motorized or by moving by hand depending on ge wanted position of the distance measuring area to the object position can be freely selected step by step or quasi-continuously.

A vertical, in the z-direction formed leg 8 of the Ge stells the means for vertical drive of the scanning head 6 , which includes the radiation source (laser) 2 and the receiver (CCD lines) 1 , on.

The scanning head 6 has a swivel drive not shown in detail.

The entire basic mechanical construction is with Schwin Provide cushioning agents in the set up was to prevent shocks of less than or equal to 3g from the inside of the device can.  

The vertical and swivel drive is designed as a spindle drive, which means that a position accuracy of less than or equal to 15 µm can be achieved. The drive of the turntable 5 consists of a flat belt lay and stepper motor. The resolving power on the periphery of the turntable is determined by the total resolving power of the axially coupled rotary encoder. B. 8196 pulses per revolution or integer divisor thereof. The different possibilities of pivoting are indicated in FIG. 2. In addition, there is the possibility that the scanning head 6 is rotated, so to speak, in the axis of the radiation source 2 .

The head swiveling in the x-y plane is one Embodiment at least ± 200, the tiltability in the x-z plane also at least ± 200.

With the device according to the invention, objects with a diameter over 300 mm can be scanned, the Scanning grid is in the range of 0.05 to 6.4 mm. The resolution solution in the measuring direction is essentially 50 µm. The wel len length of the radiation used is 670 nm and Measuring frequency 5 kHz.

The scanning object 7 is fastened on the turntable 5 with clamping means, not shown. With the help of the turntable 5 or the turntable drive, the three-dimensional object 7 rotates past the scanning head 6 in the horizontal direction. It should be noted that position sensors are advantageously provided for monitoring the functions of the drives. As already mentioned, the scanning head 6 is guided past the scanning object 7 by a vertical drive in the vertical direction. With the mentioned tilt and turn actuator, different angles of the scanning head 6 towards the scanning object 7 are adjustable.

This makes it possible to create planes parallel to the x-y plane to scan consequently, or the effects of undercut  or blind holes or similar when scanning the To avoid object.

The scanning takes place at least in an angular position of the scanning head 6 . In the case of very uneven objects, multiple scanning is expediently carried out at a constant z fixed point in different angular positions of the scanning head 6 .

Fast, coarsely screened sample scans are available for you to sample and optimization of object alignment possible.

With the device according to the invention and the associated Method for non-contact measurement of three-dimensional objects objects based on optical triangulation can be used the configuration of multiple kinematics connected surfaces can be determined. The kinemati parameters are freely selectable and can be quasi continuous be driven through. So is the rotation of the turntable lers on which the object is located, for example adjustable in steps from 0 to 4 revolutions per second. In addition, the rotary table can be moved into the measuring head direction. Swiveling and tilting or Turning the scanning head enables the cover to be captured ter areas. The grid spacing in vertical and in ob object circumferential direction is essentially 0.1 mm.

All in all, with the method according to the invention geometrically complicated and difficult to describe mathematically bare objects that have undercuts, blind holes and the like, spatially recorded with little effort , the provided 3D point data from a downstream PC or a workstation further processed can be. The fact that at most a single linear, namely a vertical drive needs to be used and egg occasionally only in a structurally simple manner  Swivel-tilt or rotary movements of a scanning head on one each vertical fixed point can be executed higher accuracy in the positioning of the scanning head, based on a given point on the surface of the measuring object.

The device according to the invention and the associated method are particularly advantageous for shoe last measurement, in Mold making in the broadest sense, with plastic injection and Printed matter, for example for toys and De signer products, including ceramic shapes and all non-cubist or free-form surfaces Chen templates, such as for orthopedic, dental and archaeological purposes that characterize an abundance of form containing measuring location data, applied.

It also makes it more arbitrary on non-physical objects non-spatial coordinate structures, e.g. B. color body or Space-time temperature bodies based on the digitization of their physical re-simulations of processes in Coordinate systems with any measurands as coordinates axes possible.

Claims (15)

1. Device for the contactless measurement of three-dimensional objects based on optical triangulation, wherein the radiation emitted by a radiation source scans the surface of the object and is reflected by this and the remission is detected by means of radiation detectors, the radiation source and the radiation detectors in a scanning head which can be moved linearly and pivoted in the z direction, are arranged with the following steps:

• - Determination of the location of the reflected radiation on at least one CCD line used as a radiation detector to determine the extent of the distance from the scanned point on the surface of the object;
• - Rotation of the object in the object distance for circumferential, ring-wise, horizontal, scanning in the x-direction of the object, with a gradual, continuous scanning in the z-direction of the object taking place after each rotation and the data obtained in this way in a ring or disc manner being stored and be used for three-dimensional reconstruction of the object by means of a data processing unit;
• - Repetition of the ring-wise scanning in a given z-scanning step at different angular positions of the scanning head when the effects of undercuts, hidden places or x-parallel planes or surfaces of the object have been detected.

2. Device according to claim 1, characterized in that means for generating a relative movement in the x-direction are provided between the rotary table ( 5 ) and the scanning head ( 6 ). 3. Apparatus according to claim 1 or 2, characterized in that the scanning head ( 6 ) can be tilted by a predetermined angular position at a selectable fixed point in the xz plane. 4. Apparatus according to claim 1, 2 or 3, characterized in that the scanning head ( 6 ) is pivotable about a predetermined angular position at a selectable fixed point in the xy plane. 5. Device according to one of the preceding claims, characterized in that the scanning head ( 6 ) has a plurality of radiation detectors ( 1 ) and imaging optics ( 3 ) for double or multiple radiation reception and for multiple triangulation. 6. Device according to one of claims 1 to 4, characterized in that the fixed points are continuously adjustable or selectable by vertical movement of the scanning head ( 6 ). 7. Device according to one of the preceding claims, characterized in that the at least one radiation source ( 2 ) is a laser diode, LED or xenon high-pressure lamp. 8. Device according to one of the preceding claims, characterized in that the radiation detectors ( 1 ) are CCD lines or other location-sensitive detectors. 9. A method for non-contact measurement of three-dimensional objects based on optical triangulation, wherein the radiation emitted by a radiation source scans the surface of the object and is remit tended by it and the remission is detected by means of radiation detectors and the radiation source and the radiation detectors are arranged in a movable scanning head, characterized by

• - A determination of the location of the reflected radiation on at least one CCD line used as a radiation detector or other location-sensitive detectors for determining the extent of the distance of the scanned point on the surface of the object;
• - A rotation of the object at the object distance to the circumferential, ring-wise, horizontal, along the y-direction he following scanning of the object, after each rotation a step-by-step, continuous scanning takes place in the z-direction and the data obtained in this way is stored and the three-dimensional Reconstruction of the object can be used by means of a data processing unit,
• - A repetition of the ring-wise scanning at a predetermined z-scanning step under different angular positions of the scanning head to avoid the effects of undercuts, hidden places or xy-plane, parallel planes or surfaces of the object.

10. The method according to claim 9, characterized, that the data processing unit three-dimensional files of the object in such a way that these files or Data via an interface from a standard CAD workstation can be processed further. 11. The method according to claim 9, characterized, that the radiation source by means of total luminous flux measurement so is adjusted that the light signal dynamics on the radiation detector is almost the same, which means the signal-noise Ver ratio of the radiation detector output signal constant ge hold and the measuring accuracy is increased. 12. The method according to claim 9, characterized, that the output signal of the at least one CCD line is analog or digitally unfolded and a focus determination for Measurement signal evaluation is carried out.   13. The method according to claim 9, characterized, that by means of a controllable focusing device Beam waist or the focus of the focused radiation depending on Measurement distance using the measurement results obtained from Environment points in real time on or in sufficient Is placed near the respective current measuring point. 14. The method according to claim 13, characterized. that the focusing device from a collimator and a to this coaxial linear actuator with low mass, high acceleration and defined damping ratio hold there, the fast focusing device like this is controlled that with control times in the ms range and well focused and with a low level of misalignment can be adjusted. 15. Device and method according to one of the preceding Expectations, marked by the use for shoe last measurement, in mold making as well for orthopedic, dental technology and archaeological Purposes.