CH675300A5 - - Google Patents

Description

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CH 675 300 A5

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description

The invention relates to a length measuring method according to the preamble of claim 1, in which an absolute scale is mapped in sections on a line sensor, the sensor signals are digitized and evaluated in a microcomputer. The method can be used in particular to carry out automatic leveling, precision leveling and distance measurement, with unequal target ranges of approximately 5 to 50 m, and can be used for positioning parts or in coordinate measuring technology.

It is known that in the case of geometric leveling, the point of penetration of the horizontal target line is visually observed through a vertical leveling staff and the measured value consists of reading the m, dm and cm and an estimate of the mm on the leveling staff.

Precision leveling involves visually coinciding on a graduation mark of the leveling staff. The measured value consists of reading the m, dm and cm on the leveling staff as well as reading the mm and fractions thereof on the micrometer.

Accidental and systematic personal errors can occur when setting, coinciding, reading and noting, especially if fatigue occurs due to the correspondingly long activity and the considerable strain on the observer. Comprehensive control calculations counteract this, although other errors can also occur here for the same reasons. The original measurement data are precompressed and transferred into a machine-readable form for further processing by electronic data processing systems. Later improvements, e.g. Graduation mark improvements to the original measurement data are therefore no longer possible. Measurement errors due to brief refraction changes can hardly be avoided.

Technical means have already been developed to relieve the observer through partial automation and to reduce errors. It is known, for example, to record the section of the measuring stick shown in the level together with a target line indicating the horizontal in the level with a film camera and to later automatically evaluate the image. For this purpose, scale lines are applied to the measuring plate, which contrast well with the other areas of the scale. Their distance from one another is known. Their distance from one end of the measuring stick is identified by a code attached to the scale line (DE-AS 1 267 855). The film is scanned perpendicular to the direction of the scale line images. A pulse generator is coupled to the scanning device. The scanning path between two scale line images or to the finish line is measured by counting the pulses. The coded marking attached to the lines is decoded with the same photocell or another one.

The fact that the recording has to be developed before each evaluation makes the method impractical and time-consuming. In addition, the accuracy of the method is limited. The pulse counter registers the number of steps until the next major change in brightness of the light-dark signals of the scale section to be evaluated. The transition range is evaluated very differently depending on the distance of the measuring stick and the conditions at the time of filming, especially since the width of the scale line must be adjusted to the greatest distance at which measurements are to be taken.

DE-OS 3 213 860 describes a measuring staff on which LEDs are arranged in the longitudinal direction of the staff at predetermined intervals, which emit coded light beams. The coding corresponds to its height on the staff. The level has a light-sensitive measuring arrangement, preferably a photo transistor, and an electrical circuit arrangement for determining the LED from which the light incident on the photoelectric sensor originates.

Compared to the technical solution mentioned above, the resolution and thus the measurement accuracy is even lower. In addition, the effort for the yardstick is very high.

Other technical solutions, which are not dealt with in more detail here, work with a level that emits beams, in particular laser beams, and scans the measuring stick with them. The technical effort for these automation solutions is very large.

DE-OS 3 427 067 describes an optoelectronic length measuring method with a coded absolute scale for absolute displacement measurement and positioning, e.g. in general machine and device construction, known. A bar code, which contains the position information of the associated scale bar, is applied to the absolute scale between the scale bars. The absolute scale is scanned in the measuring direction. A scale section is imaged on an optoelectronic line sensor (CCD line). The section always contains at least one scale bar and a complete bar coding. The line sensor is connected to a logic circuit (microcomputer). It is used to determine the fine position from the assignment of the scale bar to the line sensor and the absolute position of the associated scale bar from the bar coding.

This length measuring method can be applied to the automatic leveling with restrictions, by coding a measuring stick like the absolute scale and placing a line sensor in the beam path of the leveling. However, the resolution and measurement accuracy required for precision leveling over a large measuring range cannot be achieved. With the large number of positions to be marked, a long code word between the tick marks is required. For measurements over 50 m, the scale bar and the lines of the coding must be made relatively thick and with the appropriate space in between to guarantee the necessary resolution.

The purpose of the invention is to level 5

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to be carried out automatically while achieving a high level of accuracy.

The object of the invention is to encode an absolute scale coded in the scanning direction and to scan it with a line sensor in such a way that the position of one of many positions of the absolute scale relative to the line sensor is determined precisely regardless of the distance between the two.

According to the invention, this object is achieved in that a scale coded as a light-dark sequence is used, the section of which is shown on the line sensor, always at least two fields, one with the length 1 • £ and one with the length K • £, each in the measuring direction measured, contains, the length 1 ■ £ is the greatest or smallest length of the light-dark fields of the scale, and from the assignment of the light-dark transitions to the line sensor, both the absolute and the fine position of the absolute scale are determined.

The pixels of the line sensor arranged at a fixed distance from each other form a scale with which the field lengths can be measured and the field with the length 1 • £ can be determined. It is thus possible to determine the imaging scale, and from this the target range, and to determine the rough position of the absolute scale in relation to the position of the line sensor by evaluating the light-dark sequence of the image section.

To increase the precision, it is advantageous to determine the position of the light-dark transitions in relation to the line sensor, to compare the resulting lengths with the lengths of the light-dark fields of the absolute scale stored in the microcomputer, and to use this to determine the fine position determine, the sensor signals are preferably digitized in 16 stages.

It is preferable to use an absolute scale with a few graduation lengths between £ 0.5 and £ 2.0, for example £ 0.5 and £ 1.0 or £ 1, £ 1.5 and £ 2.0 .

This length measuring method enables precision leveling to be carried out with automatic measured value acquisition. The height positions on the leveling staff must be coded and a CCD line must be arranged in the level. The necessary accuracy is preferably achieved on the one hand by clearly coding the many positions of the graduation marks on the leveling staff with a few different lengths of the graduation marks of an uninterrupted sequence of light and dark that permit high resolution. On the other hand, as indicated in the claims and explained in more detail in the exemplary embodiment, the position of all the light-dark transitions in the illustrated cutout in the case of multi-stage digitization with respect to the line sensor is determined and made more precise by comparison with the values of the leveling staff stored in the microcomputer and the fine position is determined from this.

The finish line can be obtained by adjusting a sensitive sensor element to the image height of the horizontal finish line or by measuring and storing this height with the permanently mounted CCD line.

The method can also be used for other measuring or positioning tasks in mechanical engineering or other areas.

The invention is illustrated in more detail in the following exemplary embodiments.

Show in the drawing

1 is a level with a CCD line,

Fig. 2 shows a first leveling staff designed according to the invention and

Fig. 3 shows a second leveling staff designed according to the invention.

1 shows the known beam path of a level 1. A beam splitter 2 is installed instead of a prism. Part of the light falls through it onto an additional imaging system 3. The portion of light that passes through it is focused by the imaging system onto a CCD line 4. This sensor 4 is adjusted in such a way that the part of the image field that contains the image of the leveling staff is imaged and the target line is projected onto a predefined sensitive element, preferably a central element.

The CCD is mounted on a printed circuit board 5. On this, further electronic components are arranged, which are necessary for the operation of the line in its immediate vicinity. The circuit board 5 is connected via a cable 6 to a control and computing unit 7, an alphanumeric display unit 8 and a data memory.

The leveling mat is coded in two versions. In both variants, the graduation positions are in a linear maximum sequence (see literature reference No. 1 at the end of the description) with the period length

N = 2k '-1

encoded. With k-bit digits, N positions can be coded on the leveling staff, i.e. At least k bits must always be shown on the CCD line for unambiguous identification. In both variants, a graduation of light or dark fields with a length of 1 ■ £ is the starting point for the coding.

In the first embodiment (FIG. 2), the partial stroke size is encoded with the bi-phase code, specifically in the bi-phase space variant. Every change in brightness characterizes a bit start. The light or dark fields with the length 1 • £ have the code value 1. The additional brightness change in the middle of a field with the length 1 ■ £ indicates the code value 0. The leveling staff is with 1 • £ - and 0.5 • ^ -long fields clearly coded. The 0.5 ■ ^ long fields always appear in pairs. Further information on the bi-phase coding can be found in literature reference No. 2 at the end of the description.

In the second exemplary embodiment (FIG. 3), a delay modulation is superimposed on the linear maximum sequence. In the light or dark fields of length 1 • £ there is a change in brightness at code value 1 in the middle. With code value 0, the brightness does not change if code value 1 follows, otherwise at the end.

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The field lengths are 1 ■ £; £ 1.5 or £ 2.0. The cutout shown on the line sensor must contain at least k + 1 bits. Further information on delay modulation can be found in literature reference No. 2 at the end of the description.

In both examples, 15 positions were coded for illustration. Significantly more positions are to be displayed on an actual leveling staff. For example, 255 positions were coded on a leveling staff with the graduation mark size 1 • £ - 1 cm. Using a line sensor with 1024 pixels, the accuracy required for precision leveling was achieved in the target area of 5 to 50 m. Measurement and evaluation were carried out as follows.

The staff section shown on the CCD line is scanned and converted into a digital signal sequence by means of an AD converter. The positions of the light-dark transitions on the CCD line are determined with high accuracy from the signal sequence. The light-dark sequence is decoded and the rough position is determined from it, i.e. determined which tick mark is at the height of the target line position of the CCD line. The measured light-dark positions are compared with the (stored) values of the light-dark transitions of the measuring stick used and in the result of the comparison relative, i.e. corrected regardless of the imaging scale. From the corrected positions of the light-dark transitions shown, the imaging scale and, together with the focal length of the optical system, the target range are determined. To determine the height value, the distances between the light-dark transitions to the target position on the CCD line are determined, converted using the imaging scale, added to the height of the rough position above the base of the leveling staff, and the sums averaged. In order to further increase the accuracy and to reduce the influence of the air turbulence, especially the vertical directional scintillation, a leveling value should be determined from several image scans.

With regard to literature on the state of the art is on

1. Peterson, f.w.: Checkable and correctable codes. Munich, Vienna, Oldenburg, 1967 and

2. Schmelowsky, K.-H. u.a .: Equalization-free demodulation method for magnetic storage, part 1, in: radio fernsehen elektronik, Berlin 28 (1979) 10, p. 633 ff.

Claims (5)

1. Length measuring method with an absolute scale coded in the scanning direction and an optoelectronic line sensor, in particular for carrying out the automatic leveling, with partial representation of the scale on the line sensor, digitization of the sensor signals and evaluation in a microcomputer, characterized in that the illustrated section of a Dark sequence always coded absolute scales at least two fields, one with the length 1 ■ £ and one with the length K • £, each measured in the direction of measurement, contains the length 1 • £ the greatest or the smallest length of the light-dark fields of the scale, and from the assignment of the light-dark transitions the absolute as well as the fine position of the absolute scale is determined for the line sensor. 2. Length measuring method according to claim 1, characterized in that the sensor signals are digitized in several stages, preferably in 16 stages. 3. Length measuring method according to claim 1, characterized in that the position of the light-dark transitions with respect to the line sensor is determined, the resulting lengths are compared with the lengths of the light-dark fields of the absolute scale stored in the microcomputer, and the fine position is determined therefrom becomes. 4. Length measuring method according to claim 1, characterized in that an absolute scale with the graduation lengths 1 • £ and 0.5 • £ is used, with K = 1, or 0.5. 5. Length measuring method according to claim 1, characterized in that an absolute scale with the graduation lengths 1 ■ £, 1.5 ■ £ and 2.0 • £ is used, with K = 1.1.5 and 2.0. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 4th