Apparatus for Measuring or Setting Two-Dimensional Position Coordinates

The present invention relates to a device for measuring or setting two-dimensional position coordinates of a slide.

It is already known to provide such devices with two scales which are perpendicular (orthogonal) to each other and the extensions of which intersect in the axis of a microscope which is provided with a measurement mark. This arrangement is selected in order to be able to satisfy the Abbe comparator principle for both coordinates. Each of these scales cooperates with a reading index. In this connection it is already known to develop the reading indices such that the reading index for one coordinate direction comprises hairlines which extend over the entire measurement length of the other coordinate direction.

It is possible to arrange the scales in fixed position on a support and to connect the reading hairlines with the displaceable slide. It is also possible to arrange the reading marks fixed on the support and to displace the scales. However, in each case, it is necessary to effect a visual reading for each coordinate direction. Such visual reading is cumbersome and is subject to subjective errors.

In the case of comparators for photogrametric purposes, and where a plurality of image coordinates must be identified, the possibility of automatic measurement is particularly desirable.

An existing device to solve this problem provides the displaceable slide with two linearly ground straight edges which are arranged at right angles to each other and against which straight-edge sensors are pressed by spring pressure; these sensors cooperate with two scales, arranged at right angles to each other and in fixed position on a support. Each sensor contains a source of light, a short reading grid and a photoelectric receiver. Upon displacement of the slide, each sensor so slides along one of the straight edges that it in all cases moves along the scale associated with it. In this way, a signal is produced which serves to measure the position coordinates in known manner.

This known device has the disadvantage that precision of the measurement is affected to a substantial extent by the fidelity of the straight edges against which the sensors are pressed. Moreover, the parts which slide against each other are subject to wear, so that long-time constancy of the measuring device is not assured.

A general object of the invention is to provide an improved device of the character indicated, avoiding noted deficiencies of past devices.

A specific object is to provide a device for measuring or setting the two-dimensional position coordinates of a slide which makes it possible to effect an automatic and accurate measurement which can be reproduced at all times and which nevertheless is of technically simple and inexpensive construction.

The invention proceeds from a device in which there are provided two measurement grids which are arranged fixed at right angles to each other and the point of intersection of which coincides with a measurement mark, each of them cooperating with a reading index connected with the slide. In accordance with the invention, each reading index is developed as a scanning grid which extends over the entire measurement length of the other coordinate direction, and a photoelectric sensor for detecting the position with respect to the associated measurement screen is provided for each scanning grid. Each scanning grid consists of a plurality of hairlines extending parallel to each other, their distance apart and thickness corresponding to the associated measurement grid. In this connection, it is advisable that the scanning grid be produced by vapor deposition and that it be applied directly on the slide or on the object itself. In the measurement, the slide is moved with respect to the measurement mark. In this connection, the scanning grids move over the measurement grids, one scanning grid being associated with each measurement grid in each position of the slide. The sensors which, in case of measurement under incident light, consist only of a source of light and a photoelectric receiver, are displaced in the coordinate directions together with the slide. They therefore always give a signal which serves to count the number of hairlines (of the measurement grid) which have been traversed and which, by means of a subsequent interpolator, also enables determination of intermediate positions of measurement and scanning grids.

With the new device it is therefore merely necessary to displace the slide with respect to the measurement marks while all other components which affect the precision of measurement are fixed in position. This permits a technically simple construction with assures high constancy for a long time.

The new device can also be used for measurement in transmitted light. In this case, the source of light and the receiver are arranged on different sides of the grids.

The invention will be explained in further detail below with reference to FIGS. 1 and 2 of the accompanying drawings in which:

FIG. 1 is a basic diagram showing the principle of the new apparatus, seen from above; and

FIG. 2 is an enlarged sectional view, taken in the plane II--II of FIG. 1, with schematic indication of associated detection, signal-processing and display apparatus.

In FIG. 1, 1 is a fixed base on which two orthogonally related measurement grids 2 and 3 are so fixed in position that their point of intersection coincides with a measurement mark 4. This measurement mark may for example be physically presented to the viewer as a marking cross in the focal plane of the eye piece of an observation microscope, and therefore the numeral 1 will be understood to designate the fixed base of a microscope, and the mark 4 sill be understood to be a schematic showing of a point in the focal plane of the microscope. Each of the grids 2-3 is shown with inscribed uniformly spaced parallel markings transverse to the elongation direction of the particular grid.

A slide 5 is so arranged on the base 1 that it can be displaced only in the two coordinate directions x and y. For reasons of simplicity, details of all guide and drive elements for the displacement of the slide 5 have been omitted in FIG. 1, but they are schematically suggested by the double arrows x and y. On the slide 5 there is arranged, for instance, a photogrametric picture 6, in which picture-point coordinates are to be determined.

Two scanning grids 7 and 8 are shown with similar spaced markings which extend in the grid-elongation direction and over the entire measurement length of their respective orthogonally related coordinate directions, the same being firmly connected to the slide 5 or applied directly on it. Each of these scanning grids consists of a plurality of parallel lines, the spacing and thickness of which correspond to those of the associated measurement grid, as can be noted in particular from FIG. 2.

In the illustrative embodiment shown, the base 1 is transparent and two sensors 9 and 10 are so arranged below the measurement grids 2 and 3 in such a manner that they are displaced in the two coordinate directions together with the slide 5. Each of these sensors may consist of a source of light and a photoelectric receiver.

Upon a displacement of the slide 5 with respect to the measurement mark 4, the scanning grids 7 and 8 move over the measurement grids 2 and 3, so that in each position of the slide 5 the light coming from one of the sensors 9 or 10 passes through the associated measurement and scanning grids so as to produce a signal which directly digitally fixes the picture coordinates x and y.

The y-coordinate sensor 10 is connected with an interpolator 11 which serves for signal processing, including interpolation of the sensor signal and thus for determining intermediate positions of the y-coordinate measurement and scanning grids 3-8. Interpolator 11 supplies a digital signal, which is directly indicative of the y-coordinate (or of a change in the y-coordinate); this digital signal is fed to a suitable display or indicating device 12. In similar fashion, a digital signal which indicates the x-coordinate is concurrently developed by the sensor 9 and is fed to the indicating instrument 12 via an interpolator 13. Once correctly calibrated at the respective interpolators, the displayed x-y coordinates at 12 will always correctly locate (within slide 5) the picture point currently viewed in register with the measurement mark 4.

It will be appreciated that the described device permits very accurate measurement of two-dimensional position coordinates, it being possible to readily obtain a precision of measurement of 1.mu.m. The physical space d between adjacent opposed measurement and scanning grids (2-7, and 3-8) is largely determined by line thickness and spacing in the grids, i.e., by the desired accuracy to be obtained. The resultant spacing d can be maintained by technically simple means over a large range of displacement of the slide 5 so that, for example, point coordinates within pictures of a size of 250 .times. 250 mm can be readily measured, all without wear of measuring elements. Thus, the new device is excellently suited as a comparator for photogrametric purposes.

While the invention has been described in detail in connection with the measurement or ascertainment of coordinates for a particular point of interest within the picture or field of a slide 5, it will be understood that principles of the invention are equally applicable to the precise positioning (or repositioning) of a point within a picture or field of a slide-mounted specimen, as for example by setting an x-coordinate control (14) and a y-coordinate control (15) at the indicator 12. Thus, for the case of a given y-coordinate setting at 15, an appropriate digital-signal connection 16 to the interpolator 11 will enable the latter to make such directional and quantitative evaluation (of the setting of knob 15, in terms of the instantaneous output of sensor 10) as to enable interpolator 11 to provide a suitably poled output drive signal to y-coordinate slide-positioning means, suggested at 17. By the same token, a similar output 18 from display means 12 may provide an output control signal to the interpolator 13 for an x-coordinate drive, involving X-coordinate slide-positioning means, suggested at 19.