DD297700A5 - METHOD OF MEASURING LENGTH - Google Patents

Abstract

The invention concerns a method of measuring lengths, in which a scanning device scans a substrate (1) with a graduated scale (2), having a graduation band, and reference marks (RAK-3, RAK-2, ..., RAK, ..., RAK+3) various distances apart on at least one other band (3). The scanner signals are processed in a processing device and in a display unit, the various distances (dK-2, dK-1, dK, ..., dK+3) between the reference marks (7) being determined in graduation-band units by scanning the graduated scale from these interval-measurement signals, information is obtained in coded form on the absolute positions of the reference marks (7). The code for the absolute position of a particular reference mark (RAK) is produced by scanning two other reference marks (RAK-1, RAK-2) preceding this reference mark (RAK) in the direction of travel (8).

Description

For this 1 page drawings

Field of application of the invention

The method is applicable to translatory measuring systems, in particular high-resolution measuring systems for long lengths of machine tools and length and coordinate measuring machines.

Characteristic of the known state of the art

In machine tool and general engineering length measuring systems are used on a large scale. In principle, two types are known, one type being described by the term absolute value system and the other type by the term incremental counting system. Absolute value systems, eg CH374207, and incremental systems, e.g. B. CH499091, each have a number of specific advantages and disadvantages. A number of solutions combine the advantages of both with specific hybrid solutions and avoid their disadvantages, e.g. DT 2416212 B2 or DE 3144334C2. In the length and angle measuring device according to DE 241621282, a graduation carrier is used with a second reference track parallel to the incremental scale and identical reference marks. The reference marks can also be composed of individual stamps. The absolute value of each reference mark is determined from the respective specific distance to exactly one adjacent reference mark, these different distances between the adjacent reference marks being determined by the scanning of the increment track. To identify the individual identical reference markers. this and an adjacent reference mark must be scanned and their mutual specific spacing in units of the incremental track determined and evaluated together with the measuring direction information. At reasonable maximum distances of the reference marks, the information content of a so-coded reference track is limited. It follows that this coding is not suitable for arbitrarily long measuring systems.

In DE 3617254A1 a measuring method is realized in which at least two distances between this reference mark and two further reference marks are determined for determining the absolute value of a reference mark. This solution has the advantage that a much higher information content can be coded in reasonably small intervals over the reference marks. However, the unambiguous decoding of the different distances is more complicated and the occurring time delay between the computationally determining the two distances to this reference mark and the assignment of the absolute position to this same reference mark is greater and can limit the permissible travel speed. DE 3 324 004 A1 describes a measuring method in which, analogously to DT 2416212A1, the determination of the absolute value of a reference mark takes place by means of the decoding of the respective specific distance to an adjacent reference mark. To increase the Codierumfanges here a second parallel reference mark track is additionally introduced, which must be scanned and evaluated in parallel

 All listed measuring methods have the following defects:

The determination of the absolute value of the respective reference mark would have to take place simultaneously with the scanning of the reference mark by the scanning unit when driving over. However, a finite time is required for the decoding of the distances and the provision of the stored absolute values in the evaluation device, in particular if microcomputers are to be used for the decoding. At high travel speeds, the absolute position provided would no longer be identical to the actual position.

For application cases, in which the absolute positions, which are considered metrological raster, with variable error components, such. B. temperature error or load-dependent deformation components to be corrected by micro-computers, is not sufficient time for this correction calculation available.

Object of the invention

The aim of the invention is to improve the utility of a length measuring system, which includes a microcomputer, by increasing the Meßsignalverarbeitungsgeschwindigkeit.

Explanation of the essence of the invention

The invention has for its object to provide a measuring method for a quasi-absolute incremental length measuring system, in which a graduation carrier is scanned with abstardscodierten reference marks a reference track, and which is sufficient time between the recognition of the distance codes of the reference marks and providing the absolute position to decoding and guaranteed for correction.

The object is achieved in that in a method for measuring lengths, in which a graduation carrier having a grid division in a counting track and reference marks with different distances in at least one other track is scanned by a scanning device, wherein the scanning signals in one Evaluation device and a display device are further processed, and in which the different distances of the reference marks to each other by scanning the grid division in counting units of the count track are determined, being obtained from these distance signals information in coded form on the absolute values of the position of the reference marks, the code for the absolute value a reference mark is formed by scanning two further reference marks, which lie in the direction of travel before this reference mark. It is advantageous if the reference mark forming the code lies in the direction of travel immediately before the reference mark, which is assigned to the absolute value. The reference mark itself is therefore not part of the coding for its own absolute value.

According to the quasi-absolute incremental length measuring method according to the invention, the time is available for decoding, for auxiliary operations and for the absolute value provision, for the relative displacement of the scanning device from the moment of scanning the last reference mark belonging to the distance-coded code until reaching the reference mark, which is the Absolute value is assigned, is needed. It depends on the type of coding, whether each

such reference mark has no associated absolute value. The method makes it possible that, in a quasi-absolute incremental length measuring system, the absolute values assigned to the reference marks have been provided without time delay and thus the absolute positions provided are identical to the actual positions even at high travel speeds. Furthermore, the absolute positions of current variable error components can be assigned without influencing dos dynamic behavior of the measuring system.

Due to the time span between the code recognition and the provision of the absolute values created according to the invention, economically advantageous microcomputer solutions can be used, above all, also for the decoding of double codes and for additional correction calculations.

embodiment The invention will be explained in more detail below using an exemplary embodiment. In the drawing show

1 shows a graduation carrier with a single-coded reference track, FIG. 2 shows a graduation carrier with a doubly coded reference track, and FIG. 3 shows the arrangement of the sampling elements in the scanner.

The quasi-absolute incremental length measuring system with which the method according to the invention can be carried out

of which only a graduation carrier 1 is shown in FIG. 1, comprises a scanning device 2 scanning a reference mark track 3 and a reference mark track 3, which scanning device is connected to an evaluation device which generates electrical absolute value signals.

A scanning 4 of the scanning device shown in Fig.3 comprises a mark 5 for scanning the reference track 3 and a Countergrid 6 with four phases shifted in phase by 90 ° for scanning the grid division 2. In Fig. 1, a simple coded reference track 3 is shown, for all reference marks 7 of the reference mark track third Reference marks with absolute value assignment Ra are. The information about the absolute value of the reference mark Rak is, in the case of the forward movement, not shown Scanning device in the division direction 8 in the reference marks Rak-2 and Rak-i or at their distance d _K -i included, which

is determined by the grid division 2 by means of the derived from their count signals.

In the case of the backward movement, the information in the reference marks Rak + i and Rak + 2 or at their distance d _{K + 2}

contain. It should be noted that for information about the absolute position of the reference marks 7 in addition to the distances d and the sign according to forward (+) or reverse (-) movement heard, i. the information about the

Absolute value of Rak is in + (dx-i) and in - (d * +}). On the other hand, - (d _K -i) contains the information for Rak-3 and + (d _Kt2 ) the information for Rak + 3 · It is advantageous that z. B. at a forward movement after passing the scanner on Rak-2 and Rak-i and

the distance +! d _K -i) can be decoded on the basis of the counting signals of the raster track 2, time is available for this decoding and further correction calculations in a processor and the calculated and corrected absolute value for Rak is available before Rak is reached, and that when Rak reached this value is immediately available for the display device.

! η case of a double Kodiei tion, as shown in Fig. 2, reference marks R _{c are} included, which serve only for coding and even get assigned no absolute information. In this case, the absolute value would be for a forward movement of

Rak can be coded by + (dj_ ₂ ) and + (dj_,) and by - (d _{j + 2} ) and - (dj ₊₃ ).

Claims (2)

1. A method for measuring lengths, wherein a graduation carrier having a grid pitch with a count track and reference marks at different distances in at least one other track is scanned by a scan direction, wherein the scan signals are further processed in an evaluation and a display device, and in which the different distances of the reference marks to each other are determined by scanning the grid division in counting units of the counting track, information being obtained in encoded form from these distance signals via the absolute values of the position of the reference marks, characterized in that the code for the absolute value of a reference mark (R _Ak ) is formed by scanning two further reference marks (Raic-i, Raic-2), which lie in the direction of travel (8) in front of this reference mark (R _A k). 2. The method according to claim 1, characterized in that two further reference marks (Raic-1 'Rai (-2) are sampled, which lie immediately before the first reference mark (RaO.