WO1989001602A1

WO1989001602A1 - Sliding caliper

Info

Publication number: WO1989001602A1
Application number: PCT/DE1987/000546
Authority: WO
Inventors: René Lazecki; Alexander Witte
Original assignee: Pav Präzisions-Apparatebau Aktiengesellschaft
Priority date: 1987-08-17
Filing date: 1987-11-25
Publication date: 1989-02-23
Also published as: AU8238187A; DE3727440A1

Abstract

A sliding caliper has a first measurement part and a second measurement part that can move in a longitudinal direction (x) relative to the first part. Flat measurement electrodes (14 to 17) are electrically insulated on the first measurement part. On the second measurement part, a plurality of flat measurement counter-electrodes (33, 34) transversely arranged to the longitudinal direction (x) are passed by the measurement electrodes (14 to 17) when the first measurement part moves relative to the second measurement part in the longitudinal direction. The measurement electrodes (14 to 17) and the measurement counter-electrodes (33, 34) form a condenser the capacitance (C) of which varies according to the relative displacement of both measurement parts. In order to simplify the construction, and therefore the manufacture of the sliding caliper, and to obtain a greater degree of freedom from the point of view of the geometric design of the measurement counter-electodes, the measurement counter-electrodes (33, 34) are formed as electrically conductive surfaces (47) that extend continuously in the longitudinal direction (x) and are provided with a coating (46) of dielectric material that intermittently covers at least parts of the surface (4) in the longitudinal direction (x).

Description

Caliper

The invention relates to a caliper with a first measuring part and a second measuring part movable relative to it in a longitudinal direction, with at least one planar measuring electrode arranged electrically insulated on the first measuring part and a plurality of planar ones arranged on the second measuring part and extending transversely to the longitudinal direction Measuring counter electrodes, past which the measuring electrode moves with relative longitudinal movement of the first measuring part to the second measuring part is, the measuring electrode and the measuring counter-electrodes form a capacitor, the capacitance value varies depending on the relative movement of the two parts to each other.

A caliper of the type mentioned, in which the distance between two measuring jaws is recorded, evaluated and displayed electronically, is generally known.

If the term "slide gauge" is used in the following, this is only intended to illustrate the invention more clearly and clearly with reference to this application example. It goes without saying that the invention can also be used in other mechanical / electrical length measuring devices, e.g. also with micrometers, probes and the like.

In the known slide gauges of the type mentioned, a rotor is arranged on a rod so that it can move longitudinally. The rotor and the rod are each provided with a measuring beak projecting at 90 °, between which the object to be measured is enclosed. In order to measure the absolute position of the rotor on the rod in the longitudinal direction, conventional "electronic" calipers are provided with a capacitive measuring arrangement. This measuring arrangement consists of flat measuring electrodes, which are arranged in sliding surfaces of the rod and the rotor. These two-dimensional measuring electrodes form the two plates of a capacitor, the capacitance value of which is detected and evaluated. When the rotor is displaced longitudinally on the rod, the degree of coverage of the electrodes on the rotor and the rod changes, and thus also the capacitance value of the capacitor formed in this way. The known slide gauges are designed so that the measuring electrodes are formed as insulated electrically conductive surfaces (islands) on the rod as well as on the rotor. In practice, this is achieved by depicting the electrically insulated surfaces by vapor deposition on an electrically non-conductive base body or by inserting punched strips into a base body, which is also non-conductive, or the like.

The e.g. Measuring electrodes arranged on the rod must therefore not only be insulated from one another but also from the rod. In order to achieve a capacitor measuring arrangement, the individual measuring electrodes of the rod, which are arranged, for example, in the longitudinal direction in each case 2.2 mm long and at a distance of, for example, 2.54 mm, must be connected to one another so that the one or more electrodes of the rotor are closed each individual electrode of the rod can have a capacitive and evaluable interaction.

The known slide gauges thus have the disadvantage that they are extremely complex, in particular with regard to the arrangement of the many electrodes on the rod, because the insulation and subsequent wiring required a very complex manufacturing process. In addition, the very complex production inevitably entails a certain sensitivity to mechanical loads.

The invention is therefore based on the object of developing a slide gauge of the type mentioned at the outset which considerably simplifies its manufacture and at the same time significantly increases its robustness. This object is achieved, on the one hand, in that the measuring counter-electrodes are designed as an electrically conductive surface which is continuous in the longitudinal direction and is provided with a coating of dielectric material which at least partially discontinuously covers the surface in the longitudinal direction.

The object on which the invention is based is completely achieved in this way because the entire conductive surface, for example the rod of a slide gauge, now acts as a counter electrode. It is obvious that this greatly simplifies the manufacture of the slide gauge because only a suitable conductive surface of the rod needs to be provided with the dielectric material, for example to be glued or printed, and the rod then acts as a counterelectrode overall. A separate insulated embedding and wiring of counter electrodes is therefore no longer necessary. This also increases the robustness of the slide gauge, in which the cross section of the rod no longer has to be weakened by a groove into which the counter electrodes are then to be inserted.

Another important advantage of coating with dielectric material is that almost any shape for the counterelectrode can be chosen during coating, in particular printing.

In a preferred embodiment of the invention, the area is left in regions in the longitudinal direction without coating and forms a first reference counterelectrode there, which is opposed by a first reference electrode on the first measuring part. As an alternative or in addition, the area can be partially in Be provided with a continuous coating in the longitudinal direction and form a second reference counterelectrode there, which is opposed by a second reference electrode on the first measuring part.

The above-mentioned measures have the advantage that when the measuring parts are shifted relative to one another a reference value is generated which is independent of the longitudinal shift, one of which corresponds to the maximum capacitance value (with the dielectric coating switched on) and the other to the minimum capacitance value (without dielectric coating), these being the two extreme values between which the capacitance value between the measuring electrodes and the measuring counter-electrodes varies when the two measuring parts are shifted relative to one another. In this way it is possible to average out disturbance variables, for example the temperature dependence of the relative dielectric constant of the coating, the age dependence of the dielectric constant and the like.

The object mentioned at the outset of the invention is further achieved according to the invention in that the measuring counter electrodes are designed as a continuous, electrically conductive surface in the longitudinal direction, which is provided with recesses arranged discontinuously in the longitudinal direction.

In this way too, the object on which the invention is based can be achieved completely, because even with this solution variant the entire counter surface, for example the entire rod, acts as counter electrode and separate electrodes no longer have to be embedded in the rod. The indentations required can be introduced in a simple manner, for example by electroerosion, or they can be conversely applied to a reference surface elevations by electrode deposition. Here too, the geometric design of the measuring counter-electrodes can be varied to a certain extent, although not to the same extent as is the case when printing with a dielectric covering.

It goes without saying that in the second solution variant of the invention with discontinuously arranged depressions, reference electrodes and reference counter-electrodes in the form of continuously present or non-existent depressions can be provided over the entire length of the second measuring part.

In preferred embodiments of both solution variants, the measuring electrodes and the measuring counter-electrodes are designed as strips arranged transversely to the longitudinal direction and arranged at a constant distance from one another, as is known per se.

If the reference electrodes mentioned above are provided at the same time, a comb-like structure is created which can easily be applied or introduced in both solution variants.

It is further preferred if at least two measuring electrodes are arranged in an odd multiple of a quarter of the distance from one another in the longitudinal direction, likewise in a manner known per se.

This measure has the advantage, on the one hand, that by comparing the output signals of the two measuring electrodes it can be determined in which direction the two measuring parts are relative are shifted towards each other. Another advantage of this arrangement is that:

If, in the capacitive arrangement described at the outset, the measuring electrodes pass the measuring counter-electrodes, the result is theoretically a triangular course of the capacitance value as a function of the longitudinal displacement. The reversal points of this triangular course, that is to say the points of the longitudinal displacement at which the measuring electrodes and the counter-measuring electrodes just overlap or do not overlap, are, in practice, rounded to rounding. In order to achieve a reproducible and linear measured value here, too, one can switch to the other measuring electrode in a measuring electrode arrangement at a distance of an odd multiple of a quarter of the distance, which at this moment is in the area of greatest linearity, namely in the middle between two reversal points. In this way, a strictly linear dependency is obtained over the entire measuring range.

In a further exemplary embodiment of the invention, at least two measuring electrodes are arranged offset in an even number multiple of the distance from one another in the longitudinal direction and are electrically connected in parallel.

This measure has the advantage that a larger signal yield is possible because the effective capacitor area is doubled. This is particularly important because, in the usual dimensions of calipers, capacitance values occur in the pF range, so that the evaluable value is doubled Measurement signals means a significant simplification for further signal processing.

In further exemplary embodiments of the invention, a large number of measuring counter electrodes are provided, the extent of which is stepped in the longitudinal direction.

This measure has the advantage that a nonius-like arrangement is created, in which the increase or decrease in the surface coverage of the electrodes changes step by step, so that in this way a step-shaped signal function can be achieved as a function of the longitudinal displacement, particularly with digital evaluation means can be easily processed.

In further exemplary embodiments of the invention, the measuring counter electrodes are profiled in the longitudinal direction.

This exemplary embodiment of the invention makes use of the possibility, in particular when printing with a dielectric coating, of being able to choose the geometric design of the measuring counterelectrodes almost freely. By cleverly shaping the measuring counter-electrodes, either non-linearities can be compensated or deliberate non-linearities can be generated, for example stepped courses of the measuring signal.

In a further group of exemplary embodiments, a multiplicity of measuring electrodes are arranged at a distance from one another transversely to the longitudinal direction and can be moved over an equal number of tracks of measuring counter-electrodes. These measures, which take advantage of the variability in the design of measuring counter electrodes by printing with dielectric material, also have the advantage that the measurement result can be coded by generating a digital signal at each measuring electrode, which forms a relative or absolute signal for the respective longitudinal position of the measuring parts to one another by linking to the digital signals of the other measuring electrode.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those still explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the present invention.

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

Figure 1 is a plan view of an electrode side of a slide of a slide gauge.

2 shows a plan view of an associated electrode side of a rod of a slide gauge;

FIG. 3 shows a view of the rotor according to FIG. 1, which was placed on the slide according to FIG. 2; FIG. 4 shows an illustration in section, in the longitudinal direction, through the arrangement according to FIG. 3;

5 shows a further illustration, in section, of a variant of the arrangement according to FIG. 4;

6 to 8 three curves of measurement signals to explain the arrangement according to FIGS. 1 to 5;

9 shows a variant of an electrode arrangement for forming a vernier;

10 and 11

Signal curves for explaining the electrode arrangement according to FIG. 9;

12 to 14 three variants of electrodes profiled in the longitudinal direction;

15 is a highly schematic view of a multi-lane electrode arrangement according to the invention.

1 to 4, 10 designates a rotor of a slide gauge, which is provided with longitudinal guides 11 for a rod. The rotor 10 is provided with a first reference electrode 12 and a second reference electrode 13, which extend in the longitudinal direction x of the rotor 10 over a relatively large length section. They are preferably located Reference electrodes 12, 13 next to the guides 11 and extend over almost the entire length of the rotor 10.

Between the reference electrodes 12, 13 are a first, a second, a third and a fourth measuring electrode 14, 15, 16, 17, which are strip-shaped and extend transversely to the longitudinal direction x. The first and second measuring electrodes 14, 15 form a first pair and the third and fourth measuring electrodes 16, 17 form a second pair. The Messelek electrodes 14/15 and 16/17 of the two pairs are each offset by an equal first distance 18, which can be 4.74 mm in a practical embodiment of the invention if the extension of the measuring electrodes 14 to 17 in the longitudinal direction x each Is 2.2mm. The pairs 14/15 and 16/17 of the measuring electrodes are offset from one another by a second distance 19, which is preferably an odd multiple of a quarter of the first distance 18.

FIG. 2 shows the rod 30 belonging to the rotor 10 of FIG. 1, also in a view of the surface provided with electrodes.

2 clearly shows two comb-like structures which engage in one another and form a first counterelectrode 31 and a second counterelectrode 32 at their base, each passing through in the longitudinal direction x. The interdigitated fingers of the comb-like structures alternately form a first measuring counter electrode 33 and a second measuring counter electrode 34, specifically at a first distance 18 of, for example, 4.74 mm. As can easily be seen in connection with FIG. 4, the electrodes in the rotor 10 and in the rod 30 can be designed differently, but need not be.

The rotor 10 consists of a metallic material which is provided with an insulating insert 4.0. The measuring electrodes 14 to 17 and the reference electrodes 12 and 13, which consist of an electrically conductive material, are embedded in this insulating insert 40. The measuring electrodes 14 to 17, like the reference electrodes 12 and 13, are connected to an evaluation unit 43 by means of lines 41 and 42. The rod 30, which is also made of a metallic material, is also connected to the evaluation unit 43 via a connection 44. The evaluation unit 43 is usually located on the rotor 10 and the connection 44 is represented by the metallic contact of the rotor 10 and rod 30 on the very narrow mechanical guides 11. The evaluation unit 43 is connected to a display unit 45, for example a digital LCD unit.

As can be clearly seen from FIG. 4, the measuring counter electrodes 33, 34 are formed on the rod 30 by a coating 46 on a metallic surface 47 of the rod 30. The same applies to the reference counter electrodes 31 and 32.

In embodiments of the invention, this can be done by gluing a comb-shaped dielectric adhesive tape according to FIG. 3 to the bare surface 47 of the rod 30 or by applying a corresponding print made of dielectric material by screen printing or the like. This creates alternating capacitor areas of low capacitance (none Adhesive tape or imprint, ie air as a dielectric) and high capacity (adhesive tape or imprint with a high, realistic dielectric constant acts as a dielectric).

3 that the reference electrodes 12, 13 run continuously over the reference counter-electrodes 31, 32 when the rotor 10 is moved in the longitudinal direction x, namely that the first reference electrode 12 runs over the continuous in the longitudinal direction x, uncoated surface 47, the second reference electrode 13 would run over the longitudinal coating 46. The first reference electrode 12 with its associated first reference counterelectrode 31 therefore always shows a minimum capacitance value because the capacitor formed by the electrodes 12, 31 has a minimum capacitance value without dielectric, while this is the case with the second reference electrode 13 with the associated second reference counterelectrode 32 is the maximum value which is determined by the dielectric in the form of the continuous coating 46.

When the rotor 10 is displaced longitudinally in the longitudinal direction x, the measuring electrodes 14 to 17 alternatively travel over coated and non-coated areas of the surface 47, so that cyclically maximum and minimum capacitance values arise which are measured and evaluated in the evaluation unit 43.

The parallel connection of the measuring electrodes 14/15 and 16/17 results in capacitors of double area and thus a signal of double amplitude.

In the variant shown in FIG. 5, the design of the rotor 10 is unchanged. The rod 30a, however, is with one another of the following elevations 50 or depressions 51, so that the distance between the electrode surface of the rotor 10 and the rotor 30a fluctuates between a minimum value 52 and a maximum value 53.

In one exemplary embodiment of the invention, the depressions 51 can be formed from the surface 47 by means of electroerosion or other material-removing methods, but alternatively, an application can also be carried out by means of electrode deposition or other galvanic methods in order to produce the distance variation 52/53.

It is easy to see that when the rotor 10 is displaced longitudinally, the capacitance value also varies in this case between a minimum value (distance 52) and a maximum value (distance 53), because the capacitance value of a capacitor also depends on the distance between its planar electrodes.

Both in the electrode formation in FIG. 5 and in that in FIG. 4, signal profiles arise, as are shown in FIGS. 6 to 8.

6 shows with courses 60 and 61 the capacitance values C of the reference electrodes 12/31 and 13/32 which are invariant over the longitudinal displacement x.

7, on the other hand, shows with a curve 62 the dependence of the capacitance value C on the longitudinal displacement x in the pair of electrodes 14/33, 34 or 15/33, 34, and it can be seen from FIG. 7, that, for practical reasons, the reversal points of the theoretically triangular course are ground to a rounded minimum 63, for example.

The same applies to the course 64 of the pair of measuring electrodes 16/33, 34 and 17/33, 34 shown in FIG. 8, which is offset in the longitudinal direction x by a quarter of the first distance 18. At the location of the smoothed minimum 63 of the course 62, a straight edge 65 is therefore measured at the course 64. By selecting the more linear measurement signal, one can therefore eliminate measurement errors in the rounded areas of the courses 62, 64.

FIG. 9 shows a further variant of an electrode arrangement, in which ten measuring electrodes 70/0 to 70/9 are arranged on the rotor in an equidistant manner in the longitudinal direction x. On a rod, also equidistantly offset in the longitudinal direction x, ten measuring counter electrodes 71/0 to 71/9 are arranged, which for the sake of clarity are shown in Fig. 6 next to the measuring electrodes 70/0 to 70/9, but in the practical arrangement are below the same.

While the measuring electrodes 70/0 to 70/9 have a constant expansion in the longitudinal direction x, the length 72/0 to 72/9 of the measuring counter electrodes 71/0 to 71/9 decreases in steps, for example by 1 each / 10 of a division. If the measuring electrodes 70/0 to 70/9 and the measuring counter electrodes 71/0 to 71/9 are in an initial position, but in the position shown in FIG. 9, but with respect to one another, a maximum capacitance value is formed. If, for example, the measuring counter electrodes 71/0 to 71/9 in FIG. 9 with fixed measuring electrodes 70/0 to 70/9 are moved to the right, for example by 1/10 division, it can be seen that the overlap of the respective Surfaces linearly decreases, namely by ten times a common width 73 multiplied by the longitudinal displacement x. After exceeding a longitudinal displacement x, which corresponds to the length 72/9 of the narrowest measuring counterelectrode 71/9, the coverage decreases more slowly, because now only nine times the width 73 multiplied by the longitudinal displacement x is effective.

Overall, this results in a course 76, as shown in FIG. 10, which is formed from a series of straight pieces 77 of decreasing incline.

If the course 76 is differentiated according to FIG. 10, a staircase function 78 as shown in FIG. 11 is obtained. Such a staircase function 78 has the advantage in digital signal evaluation that the transition points can be identified more easily than with a continuous signal curve by means of digital comparators.

The arrangement of FIGS. 9 to 11 thus forms a vernier in which the area coverage and thus the capacitance value within a measuring point changes with the units of the respectively lower measuring point in an easier to evaluate manner.

FIG. 12 shows a measuring counterelectrode 79 which is provided with a profile 80 in the longitudinal direction x in order in this way to achieve non-linearities, for example as in the case of the ground ones Mini a 63 in Fig. 7 to compensate or to generate desired non-linearities.

13 shows a further measuring counterelectrode 91, which is provided with a step profile 82 in the longitudinal direction x, in order in this way likewise to produce a stepped course of the capacitance value C.

Fig. 14 shows a further measuring counterelectrode 85 with a continuous continuous staircase profile which can pass over the entire length of the rod 30.

Finally, FIG. 15 shows a further arrangement in which four measuring electrodes 90/0 to 90/3 are arranged offset on the rotor transversely to the longitudinal direction x. Each measuring electrode 90/0 to 90/3 has a path of measuring counter electrodes 91 which are discontinuously applied in the longitudinal direction x as strips. The measuring electrodes 90/0 to 90/3 are connected to a decoder 92, which determines an absolute or relative position of the rotor on the rod from the signal present at each measuring electrode 90/0 to 90/3 and from their logical combination with one another. The arrangement of the measuring counter electrodes 91 can e.g. be selected so that a two-off-four code, a BCD code or another suitable code results on the measuring electrodes 90/0 to 90/3 when the rotor moves on the rod and on the measuring electrodes 90 / 0 to 90/3 due to the logical pattern of the measuring counterelectrodes 91 alternatively a high or a low capacitance.

Claims

1. caliper with a first measuring part and a second measuring part movable relative to it in a longitudinal direction (x), with at least one planar measuring electrode (14 to 17; 70; 90) which is arranged in an electrically insulated manner on the first measuring part and a plurality of arranged in the second measuring part and extending transversely to the longitudinal direction (x) planar measuring counterelectrodes (33, 34; 71; 79; 81; 85; 91, past which the measuring electrode (14 to 17; 70; 90) upon relative longitudinal movement of the first measuring part relative to the second measuring part, the measuring electrode (14 to 17; 70;

90) and the measuring counter electrodes (33, 34; 71; 79; 81; 85; 91) form a capacitor, the capacitance value (C) of which varies depending on the relative movement of the two measuring parts to one another, characterized in that the measuring counter electrodes (33, 34; 71; 79; 81; 85;

91) are designed as an electrically conductive surface (47) which is continuous in the longitudinal direction and which has a coating which at least partially discontinuously covers the surface (47) in the longitudinal direction (x)

(46) is made of dielectric material.

2. Caliper according to claim 1, characterized in that the surface (47) in some areas in the longitudinal direction (x) is left without a coating (46) and forms a first reference counterelectrode (31) there, which is opposed by a first reference electrode (12) on the first measuring part.

3. caliper according to claim 1 or 2, characterized gekenn¬ characterized in that the surface (47) in some areas in the longitudinal direction (x) with continuous coating (46) is provided, and there forms a second reference counter electrode (32) on the first measuring part there is a second reference electrode (13).

4. caliper with a first measuring part and a relative to it in a longitudinal direction (x) movable second measuring part, with at least one on the first measuring part arranged electrically isolated, area measuring electrode (14 to 17; 70; 90) and a variety of on arranged second measuring part, extending transversely to the longitudinal direction (x), planar measuring counter electrodes (33, 34; 71; 79; 81; 85; 91), - past which the measuring electrode (14 to 17; 70; 90 ) is moved with relative longitudinal movement of the first measuring part to the second measuring part, the measuring electrode (14 to 17; 70) and the measuring counter-electrodes (33, 34; 71; 79; 81; 85; 91) forming a capacitor, the capacitance value ( Z) varies as a function of the relative movement of the two measuring parts to one another, characterized in that the measuring counter electrodes (33, 34; 71; 79; 81; 85; 91) as an electrically conductive surface (47) which is continuous in the longitudinal direction (x) are formed with the in longitudinal direction Attention (x) discontinuously arranged depressions (51) is provided.

5. caliper according to claim 4, characterized in that the surface (47) in some areas in the longitudinal direction (x) is left without a recess (51) and forms a first reference counter-electrode (31) there on the first measuring part a first reference electrode ( 12) faces.

6. caliper according to claim 4 or 5, characterized gekenn¬ characterized in that the surface (47) is partially in the longitudinal direction with a continuous recess (51) and there forms a second reference counter-electrode (32) on the first measuring part is opposed by a second reference electrode (13).

7. Caliper according to one of claims 1 to 6, characterized in that the measuring electrodes (14 to 17) and the measuring counter-electrodes (31, 32) are arranged as strips arranged transversely to the longitudinal direction (x) and at a constant distance (18th ) are arranged to each other.

8. caliper according to one of claims 1 to 7, characterized in that at least two measuring electrodes (14/16 15/17) in an odd multiple of a quarter of the distance (19) to each other in the longitudinal direction (x) are arranged offset.

9. caliper according to one of claims 1 to 8, characterized in that at least two measuring electrodes (14/15 16/17) in an even multiple of the distance (18) to each other in the longitudinal direction (x) arranged offset and electrically connected in parallel.

10. caliper according to one of claims 1 to 9, characterized in that a plurality of measuring counterelectrode (71/0 to 71/9) is provided, the extension in

Longitudinal direction (x) is stepped.

11. Caliper according to one of claims 1 to 10, characterized in that the measuring counter electrodes (79; 81; 85) are profiled in the longitudinal direction (x).

12. Caliper according to one of claims 1 to 10, characterized in that a plurality of measuring electrodes (90/9 to 90/3) are arranged at a distance transversely to the longitudinal direction (x), which over a same plurality of webs of measuring counter electrodes (91 ) are movable.