Device for producing reference signals

(42) Date of commencement of the patent: 15. 4.1993 (45) Date of issue: 27.12.1993 (73) Patent owner:

RSF ELECTRONICS SOCIETY Μ. BH A-5121 TARSDORF, UPPER AUSTRIA (AT).

(54) REFERENCE SIGNAL GENERATION DEVICE (57) In a photoelectric signal generating apparatus, especially in measuring systems, is on a relative to one with photoreceivers (6, 7) equipped scanning unit adjustable support (1) an illuminable, at least one reference point characterizing mark (9 to 11) provided which causes a characteristic change 'in the reference point of the occurring scanning signal, which can be evaluated for generating a reference signal. The marking consists of at least two marking strips (9, 10) provided in scanning paths offset transversely to the adjustment direction, one of which extends in its track to the reference point (11) and the second extends from the reference point, the marking strips (9, 10 ) overlap one another in the region of the reference point (11) __. The scanning unit has at least one photoreceiver (6, 7) aligned with it for each track, and the photoreceivers are offset in the adjustment direction and connected in antiparallel connection according to the length of the overlap, so that their sum signal in the region of the reference location is an eg having a window comparator (8) detectable, the reference signal defining zero crossing.

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AT 396 840

WRewasis

The invention relates to a device for generating reference signals by photoelectric means, in particular in measuring systems, wherein an illuminable, at least one reference point characterizing mark is provided on a relatively equipped with a photoreceptor scanning unit adjustable carrier at the reference point a characteristic change of the scanning signal occurring causes, which is evaluable for the generation of a reference signal

Reference signals are required, among others, in incremental measuring systems, in order to be able to relate the respective measurement to clearly defined scale positions and to a specific position after interruptions in operation, power failure, etc. to clearly find again. With Drehgcbem a revolution counter can be additionally controlled by a reference signal. It is necessary to generate a reference signal so that it is assigned as clearly as possible to an edge of a division field in the case of incremental divisions. Furthermore, it is desirable that the displacement path in which a reference signal occurs is equal to or smaller than the displacement during a counting step in incremental measuring systems.

In a known device of the type mentioned above, the mark indicating a reference point consists of a non-periodic grating pitch, in the case of incremental measuring systems, where the smallest bar width is in a defined ratio to the graduation scale, an associated photoreception «against the scanning track, in which the mark lies, is directed and scans this track through a corresponding grating pitch as the brand having scanning through, so that depending on whether strongest illumination or darkening occurs at the reference point if the markings and the scanning plate coincide characteristic signal peaks occur up or down, which can be evaluated directly as a reference signal. A disadvantage of the known construction is that the attachment of the reference marks in exact assignment to a measuring scale is expensive, with no corrections made the relative position of the signal occurring to the carrier w 'can and that a certain relatively small distance between scale and scanning are not exceeded may.

Is z. If, for example, the interval of the scale graduation of an incremental scale is 20 pm and the smallest line width of the reference marking g = 15 gm, then a distance (d) of

2g² d = - = 511 gm

Z are exceeded, where χ is the centroid wavelength of the light emitted by the light source used in the known reference marks can also not determine from the scanning signal, from which side z. B. the scale forth a reference mark is approached or on which side of the sampling is the reference mark

The object of the invention is to provide a device of the type mentioned, which, with a simple construction, enables the exact generation of specific reference signals assigned to specific scale positions, is insensitive to changes in the scanning distance and relatively large scanning distances, allows subsequent corrections for the determination of the reference point and, moreover, specify the relative position of the current sampling point relative to the reference point (right or left of the reference point).

The task is solved in principle by that the marking consists of at least two marking strips provided in scanning directions offset transversely to the adjustment direction, of which one passes in its lane to the reference point and the second continues from the reference point, wherein the marker strips overlap each other in the region of the reference point, in that the scanning unit has at least one photoreceiver oriented for each track, and that the photoreceivers are offset in the adjustment direction according to the length of the overlap and connected in anti-parallel connection, so that their sum signal in the area of ​​the reference point z. B. Having detected by a window comparator, the reference signal defining zero crossing

In the case of a scanning unit located outside the reference point, only one of the two photoreceptors generates a characteristic signal, so that solely from this, which receiver generates a signal or The signal shape of the resulting sum signal is due to the size of the overlap of the marking strips at the reference point and the edge shape, in particular the shape of the end edges of the marking strips in cooperation defined with the shape of the reception fields of the photoreceptor or definable. It can be at the reference point produce a relatively steep signal edge with zero crossing, with minor changes in the position of the reference point can be made by slight changes in the distances of the photoreceptor on the one hand and by adjusting the trigger points of the window comparator on the other hand. By adjusting the trigger points of the window comparator, the pulse width can also be precisely defined. Another possibility is to set only one trigger point and to trigger a stored, preselectable signal having reference pulse via the trigger signal.

-2AT396840B

It has already been mentioned that the form of the summation signal obtained is determined by the shape of the mark, the size of the overlap at the reference site and the shape of the receiving areas of the photoreceivers, which can also be determined by normal photoreceptors. Accordingly, it is also preferable to choose other shapes of the ends of the marking strips in the case of round receiving surfaces than in the case of rectangular receiving surfaces. For indicating the relative position of the scanning unit to the reference point is sufficient for outside of the reference point sampling unit, a relatively weak signal, whereas in the area of ​​the reference point often desires a more pronounced upper and lower signal level, between which the zero crossing takes place to more room for the trigger points and to obtain an even more pronounced change of the signal curve in the region of the reference point.

To achieve this, envisages a further education, that the marking strips in the overlapping area are widened after the side directed to the other track, so that in the dimensions adapted to this broadening photoreceptors when entering the overlap region, a signal increase occurs thereby it is possible, the marking strips with larger distances from each other, about to provide on the two sides of a incremental graduation in corresponding measuring systems. However, it is more advantageous if, according to a preferred embodiment, the two tracks are provided next to one another and the marking strips merge into one another in the overlapping area. At present, an embodiment is preferred in which the overlap region is in the form of a rectangle whose scan-direction edges merge into the outer edges of the marker strips and the receiving surfaces of the photoreceptors have an adapted rectangular shape but terminate transversely in front of the unassigned track.

In the embodiment described so far, only one reference signal should be generated at a certain point. Will you z. B. unambiguously define several reference points on a scale, you can assign each of these reference points a mark of the type described. It will then prove necessary, however, to provide switching measures between successive reference points, for example via a scanned control track, in the necessary because of the staggered arrangement of the photoreceptor jump from the then z. B. to prevent the triggering of a reference signal between the lower scanning mark ending two reference marks on the upper scanning mark starting there. It would also be possible to arrange the marking with marking strips passing between the reference points, but it is then necessary to provide two pairs of photoreceptors with photoreceptors offset in the same manner for each pair and to use only one pair for the triggering of the reference signal.

Further details and advantages of the subject invention is taken from the following description of the drawing.

In the drawing, the subject invention is for example illustrated It show

1 is a schematically diagrammatic representation of an embodiment of a device according to the invention realized in an incremental measuring system,

Fig. 2 shows a second embodiment in the Fig. 1 corresponding representation and

Fig. 3 is a graph of the occurring sum signal.

From an incremental length measuring system, only one scale body (1) with incremental graduation (2) was indicated. The also the measuring graduation (2) scanning in transmitted light scanning unit is additionally associated with a lighting device (3), which may consist of an LED, incandescent lamp or laser diode and their light, which is directed by a condenser lens (4) in parallel, against the next incremental graduation (2) lying area (5) of the scale body (1) blasted. On the opposite side of the scale body are, preferably integrated into the scanning unit for the incremental graduation (2), two associated mutually offset photoreceivers (6), (7), which are connected to an evaluation unit (8), wherein initially an anti-parallel connection of the outputs the two photoreceptor (6), (7) made and the resulting sum signal is fed to a window comparator.

In area (5) of the scale body is shown in FIG. 1 an opaque cover provided in which two transparent marking strips (9), (10) are recessed, which merge into one another in the region of a reference point of the scale in the form of a rectangular window (11). The photoreceiver (7) is assigned to the marker strip (9) shown in the drawing above and the photoreceiver (6) to the marker strip (10), wherein the photoreceptor within the window (11) in the direction of the other strip (9) or (10) extend over a portion of the window, but at no point but the other marking patches (9) or (10) reach. In the longitudinal direction, ie in the direction of the relative adjustment of the scanning unit relative to the scale body (1) the photoreceivers (6), (7) are offset depending on the window width, so that only at one point both receivers (6), (7) illuminated the same be in any other position of the scanning unit but one of the two photoreceivers receives more light than the other and outside the window only one of the two photoreceivers is illuminated.

The same conditions arise in the embodiment of FIG. 2, where working in reflected light and instead of the light-transmitting region of FIG. 1 a the same shape as the markers (9), (10)

-3AT396840B and the window (11) having reflective mark is provided, in which the corresponding parts are identified by an additional line. The illumination unit (3 '), (4') is located on the same side of the scale body (1 ') as the photoreceivers (6'), (7 *).

If the scale body (1), (1 ') relative to the scanning unit with illumination device (3), (4) and photoreceptors (6), (7) in the direction of arrow (12), (12') adjusted and is the scanning unit even before the Referenzstefle, then initially only the photoreceiver (7), (7 ') on the marker strip (9), (9') illuminated, so that the sum signal of the two photoreceivers (6), (7) through the curve section (13) in FIG. 3 reached level shown reached. When the photoreceivers (7), (7 ') in the window (11), (11 ') this level rises to (14) and reaches the upper value (15), when the photoreceiver (7), (7 ') in the fully over the window (11), (11 *) illuminated position now reaches the photoreceiver (6) during the further adjustment, (6 ') the window (11), (11 *), Thus, the signal decreases with a steep edge (16) and shows a characteristic zero crossing, as soon as both photoreceivers (6), (6 '), (7) (7 ') are equally illuminated over the window. From then on, the illumination of the photoreceiver (7), (7 *) and those of the photoreceptor (6), (6 ') to, until finally, if the photoreceiver (7), (7 ') from the window area (11), (11 *) has resigned, only the photoreceptor (6), (6 *) in the window (11), (11 ') is lit, so that the signal to the course (15) opposite course (17), with increasing leakage also of the photoreceptor (6), (6 ') shows the (14) opposite course (18) and finally the course (19), if only the photoreceiver (6), (6 ') on the scanning track (10), (10 ') is aligned. In Fig. 3 were still the adjustable trigger points (20), (21) of a window comparator drawn over the example, the slender square wave signal (22) is generated as a reference signal.