GB2041690A

GB2041690A - Optical method for measuring distances and contours

Info

Publication number: GB2041690A
Application number: GB8002870A
Authority: GB
Original assignee: HA Schlatter AG
Current assignee: HA Schlatter AG
Priority date: 1979-01-31
Filing date: 1980-01-28
Publication date: 1980-09-10
Also published as: CA1140333A; GB2041690B; FR2448125A1; ES488053A1; NL8000561A; DE2903529A1; JPS55103403A; SE8000727L

Abstract

A method for measuring distances and for determining the three- dimensional contour of a workpiece, which includes directing two intersect- ing light beams (3,4) onto a workpiece (12) to be measured, determining the light points (13,14) produced by the beams on the workpiece surface and measuring the angles ( alpha , beta ) of inclination of the striking beams in their common plane. The laser light beams (3,4) may be scanned along a contour (12) by means of pivotting coupled mirrors (5,6) and the light spots (13,14) position determined by photodiode screens (17,18), the beams being of different colours to be separated by a dichroic mirror (16), or one beam may be scanned much faster than the other and the inclination valves ( alpha , beta ) taken when the two spots coincide. <IMAGE>

Description

SPECIFICATION Method for measuring distances and apparatus for performing the method The invention relates to a method for measuring distances and for determining the three-dimensional contour of a workpiece and also relates to apparatuses for performing the method.

When measuring distances and when determining the three-dimensional contour of a workpiece it is known to use mechanical calipers, which determine the distance or scan the three-dimensional contour of a workpiece. The scanned values are converted into electrical signals by transducers and these signals are then indicated or stored. These measuring methods are time-consuming and can only be used if the distance to be measured is within the given range or the contour to be determined permits a mechanical scanning. It is also known to measure distances electronically or electron-optically. The microwaves or light waves emitted by a transmitter are reflected and collected by a receiver. The phase difference between the emitted and the received wave serves as a measure for the distance.However, such measuring method are complicated and are only used when measuring long distances.

The object of the present invention is therefor to so further develop a contactless distance measuring method that it is possible in a simple manner to measure distances and three-dimensional contours in the range of up to a few metres.

According to the present invention a method for determining the three-dimensional contours of a workpiece includes directing two intersecting light beams onto a workpiece to be measured, determining the light points produced by the beams on the workpiece surface and measuring the angle of inclination of the striking beams in their common plane.

The invention also includes apparatus for performing the method set forth and which comprises means for producing two light beams, two spaced apart mirrors struck in each case by a single beam, a collecting optics and at least one light-sensitive screen arranged behind the collecting optics and means for measuring the position of the mirrors.

The present measuring method is particularly suitable for operating devices for recognising opticals which are noÇprogrammed in and for determining the distance, shape and position of workpieces, which are to be determined by the operating device and whose contour has previously been electronically stored.

The invention can be performed in various ways but two embodiments will be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a first embodiment of apparatus for performing the method, and Figure 2 is a diagrammatic representation of a second preferred embodiment.

In the embodiment shown in Figure 1 the apparatus comprises two laser beam generators 1, 2 which generate light beams 3,4 which have different wavelengths, for example the light beam 3 can be blue and the light beam 4 red. The twolight beams 3, 4 are defiected by mirrors 5, 6 and intersect at a point 7. To this end, the two mirrors 5, 6 are slightly inclined towards one another. Mirrors 5,6 can be rotated about points 8,9 and are articulated to a common swivel mechanism 10. The swivelling movement of the two mirrors 5, 6 is performed by a motor 11. In this way, the mirrors 5,6 perform a reciprocating swivelling movement, the particular mirror positions being read electrically by the motor 11.

The two intersecting beams 3,4 strike a workpiece surface 12 at different points. The impact point of the blue beam 3 being indicated by the reference numeral 13 and that of the red beam by 14.

These light points are determined by a collecting optics 15 and are projected onto a semi-transparent mirror 16. This semitransparent mirror separates the light in accordance with the different wavelengths, for example the blue light is permitted to pass through and the red light is reflected. A photodiode screen 17 is positioned behind the semitransparent mirror 16 inclined by 45". A further photodiode screen 18 is positioned at right angles to the first screen.

In this way, the blue light point 13 is imaged on screen 17 and the red light point 14 on screen 18. The distance on the workpiece contour 12 between points 13 and 14 can now be calculated through the position of mirrors 5,6, whose value is read by motor 11 and bythecoordinatesoftheimaging points on screens 18, 17.

If the workpiece contour 12' is nearerthe measuring device, then in the case of the same mirror position the light points 13', 14' are closer together, so that the coordinates of the imaging points on the screen 17, have changed. In this way, it is possible to calculate the distance and contour along a coordinate.

The complete measuring apparatus is pivoted along an axis 19, so that the contours parallel to contour 12 can also be determined. However, it is also possible to provide a further swivelling mirror arrangement, as will be described hereinafter in conjunction with Figure 2.

In the embodiment of Figure 2, only one laser beam generator 20 is provided. The laser beam generated by it strikes a rigidly arranged semitransparent mirror 21, which permits the passage of part of the beam and reflects a further part thereof.

The reflected beam portion strikes a mirror 22, whilst the beam portion which has passed through strikes a mirror 23. Mirror 22 is pivoted at 24 and mirror 23 at 25, and they are connected in each case to separate swivel drives 26, 27 by lever arms. The position of each mirror is read electrically through the position of the swivel drives 26,27. The measuring apparatus has a collcting optics 28 and photodiode screen 29.

The swivel drive 27 moves rapidly, whilst swivel drive 26 moves slowly in comparison therewith. This means that the beam 30 reciprocates rapidly and beam 31 reciprocates slowly. Thus, beam 30 moves along beam 31. The two beams 30,31 strike the material surface 32 where they produce separate light points. The latter are imaged on screen 29. If the beams 30, 31 intersect on material surface 32 a common impact and intersection point 33 is obtained. Correspondingly, only one imaging point 34 is formed on screen 29. In this case, i.e. if screen 29 only records a single imaging point 34, a call signal is given by screen 29 which determines the position of the swivel drives 26,27 at this moment and consequently the position of mirrors 22,23. The position of mirrors 22,23 is a measure of the distance from impact point 33.The contour 35 of workpiece surface 32 can be scanned with this arrangement.

For scanning the adjacent contour 35' a further swivel mirror 36 is provided and the beams reflected by mirrors 22,23 strike mirror 36 and are then reflected again. The position of mirror 36 is determined by a swivel drive 37.

If the semitransparent mirror 16 shown in Figure 1 does not perform a colour separation a red and a blue filter 38, 39 can be positioned in front of the relevant screen 17,18.

The angular position a and ss of the beam striking the material surface and the coordinates of the imaging points 13, on screen 17, or the coordinates of the imaging points 34 of the intersection point 33 on the screen 29 are important for the present method.

In the embodiment according to Figure 1, the angles a and ss are directly related with one another due to the common swivel mechanism. Thus, a particular angular position a and ss is associated with each swivel mechanism position. Thus, the distance between points 13 and 14 determined by the imaging coordinates on screen 17,18 defines the distance between the measuring device and contour 12 for a given angular position a, ss. Thus, for distance measurements a given position of the swivel mechanism is determined which corresponds to a given angular position a, ss and the imaging coordinates of points 13, 14 are measured.The position of the swivel mechanism and the imaging coordinates are fed into a computor which, for the particular angular position a, 13 calculates the distance between points 13 and 14 and from said distance value and the angular position a, ss calculates the distance between the measuring device and points 13, 14.

If this is performed for successive angular positions a, 13 the computer calculates the distance of the measurement device from each point of contour 12 and consequently also the course of the contour.

This procedure can be performed in punctiform digital or continuous analog manner.

In the embodiment of Figure 2, the particular angular position a, ss is determined when the beams 30,31 intersect on contour 35, i.e. only one point appears on the screen 29. The distance between the measuring device and point 33 is then calculated from the values a and (3which are supplied to a computor. The processing of the coordinates of imaging points 34 is not necessary, but can be carried out in order to increase the reliability of the measurement. If the said distance measurement is performed along the contour 35, it is possible to determine the distance of each point on contour 35 and consequently also the course of the actual contour.

Claims

1. A method for measuring distances and for determining the three-dimensional contour of a workpiece, which includes directing two intersecting light beams onto a workpiece to be measured, determining the light points produced by the beams on the workpiece surface and measuring the angle of inclination of the striking beams in their common plane.

2. A method according to claim 1, wherein the beams are pivoted in their common plane.

3. A method according to claim 2, wherein the change in the angle of inclination of both beams is the same and the position of the light points is measured.

4. A method according to claim 2, wherein the angle of inclination of one beam is varied slowly in relation to the angle of inclination of the other beam which is varied relatively rapidly, and the inclination angles of the striking beams are measured when they intersect on the material surface and form their common light point.

5. A method according to any one of the claims 1 to 4, wherein the common plane of the beams is pivoted into a plane perpendicular thereto.

6. An apparatus for performing the method according to one of the claims 1 to 5, comprising means for producing two light beams, two spaced apart mirrors struck in each case by a single beam, a collecting optics and at least one light-sensitive screen arranged behind the collecting optics and means for measuring the position of the mirrors.

7. An apparatus according to claim 6, wherein the mirrors are swivelled by a common swivelling mechanism, the beams have different wavelengths and a semitransparent mirror is arranged behind the collecting optics which permits the passage of part ofthe light two afirstscreen and reflects another part of the light onto the second screen.

8. An apparatus according to claim 6, wherein the mirrors are swivelled by separate swivelling mechanisms and the position thereof is measured when a single light point is received on the screen.

9. An apparatus according to one of the claims 6 to 8, wherein a further swivelling mirror is provided which deflects the beams from the two mirrors and means for measuring the position thereof.

10. An apparatus according to any one of the claims 6 to 9, wherein the beams are laser beams.

11. An apparatus according to claim 7 and claim 10, wherein two laser beam generators are provided which generate light with different wavelengths.

12. An apparatus according to claim 8 and claim 10, wherein one laser beam generator is provided and a fixed semitransparent mirror is provided between the generator and two other mirrors.

13. An apparatus according to any one of the claims 6 to 12, wherein the screen is a photodiode array.

14. An apparatus according to any one of claims 6,7, 10, 11 or 13, wherein the semitransparent mirror separates the light into two wavelengths.

15. An apparatus according to claim 7, wherein a filter is provided in front of each of the screens and one filter permits the passage of light of one wavelength and the other permits the passage of light of the other wavelength.

16. A method of measuring distances and for determining the three-dimensional contours of a workpiece substantially as described herein with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

17. Apparatus for performing the method set forth in claims 1-5 and claim 16 substantially as described herein with reference to and as shown in Figure 1 and Figure 2 of the accompanying drawings.