Position-measuring device with plural probe placings.

The invention relates to a position measuring device according to the preamble of claim 1.

In the position measuring measurement results can be improved if the material measure is scanned with a plurality of scanning devices at a plurality of sampling positions.

Known are such position measuring systems for example from US-A-4,580,046 and US-A-4,580,047. There, the speed of movement of components to be measured and the phase position of the measurement signals is monitored by means of clocked test circuits, each encoder will be double scanned.

From DE-A1-35 27 128 a rotational speed-measuring arrangement is known in which the amplitudes of the measuring signals should be kept constant. The encoder described there has two 180 ° spatially offset signal generator in the form of light barriers, the two 90 ° staggered generate sinusoidal voltages, from which is determined by averaging the angle of rotation.

Furthermore, from DE-A1-27 11 593 a tachometer, in which a tone wheel is scanned by two spatially mutually offset by 180 °, light barriers. There, too, the output signals are combined and averaged.

With these so-called double sampling eccentricity and mechanical pitch errors can be reduced. In this case, phase shifts can be tolerated between the sampling signals delivered by the two sample locations to a certain degree. However, if a limit is exceeded, there is a risk that the resulting signals are too small or cancel each other out completely. Using a vectorial representation of the scanning, this is to be explained later.

The danger of the limit value is exceeded is particularly with large accelerations by shock or excessive vibration. In this case, the double sampling - the yes is used in normal operation to increase the measurement accuracy - disadvantageous because the signals of a scanning point to extinguish the signals of the other scanning point completely or at least partially, which can lead to counting errors.

The invention has for its object to provide a position measuring device with multiple scanning, which may not come to miscount when vibrations or the like.

This object is achieved by a position measuring device having the features of claim 1.

The advantages of the position according to the invention are that it uses in normal operation, the positive effects of the multi-scanning, which are expressed in more accurate measurements without the disadvantages of the multi-scan must be taken at high accelerations by shock or vibrations in purchasing.

The invention is illustrated hereinafter by means of embodiments with reference to the drawings in more detail.

It shows<ul><li>Figure 1 shows a block diagram of a position with two scanners;</li><li>figure 2 a) a circuit for differential signal formation with two scanners; b) a circuit for differential signal formation with four scanners;</li><li>figure 3 a) a circuit for generating absolute values ​​at two sampling; b) a circuit for generating absolute values ​​at four sampling;</li><li>figure 4 a) a circuit for summing variable signal weighting at two scanning devices; b) a circuit for summing variable signal weighting at four sampling;</li><li>figure 5 a) - e) various phase diagrams.</li></ul>

The block diagram shown in Figure 1 shows two samplers 1 and 2, which scan a graduated disk 3 of a rotary encoder, not shown. The part of plate 3 is mounted on a shaft fourth Part wheel 3 and shaft 4 facing each other a certain eccentricity "e" on. The disc part 3 has an incremental graduation 5, are generated by the two phase-shifted by 90 ° by means of the scanning devices 1 and 2, scanning signals U1, U2 and U3, U4. The phase shift of the scanning signals U1 and U2 is used in a known manner to determine the direction of rotation of the index wheel 3. As the scanning devices 1 and 2 are diametrically opposite, is called spatially by 180 ° phase-shifted scanning locations A1 and A2.

To measure the rotation angle of the disc part 3 in each case, the scanning signals U1 and U3, and U2 and U4 are analogous added and averaged thereby. This reduces the normal operation, the influence of the eccentricity "e" on the measurement result.

However, the double sampling also has its limits, as the eccentricity "e" by vibrations, strong accelerations briefly exceeds by impact or the like the allowable limit. This can lead to counting errors, since the scanning signals U1 and U3 or U2 and U4 even canceled in the analog addition in extreme cases.

To make the miscount danger understood was here briefly to Figure 5, in which the analog addition in five randomly selected different phase relationships between the scanning signals U1 and U3 of the scanners are 1 and 2 by means of phase diagrams, and in which the resulting signals Sr according are shown the prior art in broken lines and the resultant signals Sr 'according to the invention with solid lines.

Figure 5a shows the case that there are no phase shift between the sampled signals U1 and U3 of the scanning devices 1 and 2. FIG. The two scanning signals U1 and U3 add up to 2 x U1 and the measured value is correct.

In Figure 5b the phase shift 2α between the scanning signals U1 and U3 is about 60 °, so that the resulting signal Sr 60 a signal · U1 cos is 30 ° available from 2 amount. This phase shift is still within the permissible tolerance range.

The phase diagrams of the figures 5c show to 5e, as the resulting signal Sr deteriorated gradually until it 5e in the presentation to the extinction comes. So in this case it would ensure a miscount.

In order to avoid this, the Ab are according to the invention in case of malfunction sensing signals weighted differently. With the circuit shown in Figure 1 of the fault can be determined and the different weighting of samples are carried out, so that it comes to the resulting signals Sr 'according to FIG. 5

The 0 ° scanning signal U1 of the first scanner 1 and the 0 ° scanning signal U3 of the second pickup 2 are to a difference-forming element D1 supplied in the from the two 0 ° -Abtastsignalen U1 and U3, a differential signal U6 is formed.

Similarly, a differential signal U8 from the two 90 ° -Abtastsignalen U2 and U4 is formed in a difference-forming element D2, which are fed by the scanners 1 and 2 in the difference-forming element D2.

The 0 ° -Abtastsignale U1 and U3 are also a summer S1 and 90 ° -Abtastsignale U2 and U4 a summing S2 supplied. In the summers S1 and S2 will later reference.

In Figure 2a, the difference-forming blocks are shown schematically D1 and D2, such as are required for two scanning devices 1 and 2. FIG. The difference signals U6 and U8 are two phase-shifted by 90 ° signals again.

2b shows a difference-forming block D4 is shown as it would be required in a non-illustrated rotary encoder with eg four scanning locations A1 to A4. For multiple sample points A1 to A4, the differences between the signals of "Hauptabtaststelle" and the corresponding signals of the other sampling points are formed. Thus, eg, with four sample locations three 0 ° - and three 90 ° -Differenzsignale. Is the eccentricity of 0, the signal differences are also 0th

After subtraction of the difference-forming blocks D1 and D2, the 0 ° - and the 90 ° -Differenzsignal U6 and U8 amounting educational block B supplied. One way to design the amount educational block B is the circuit to be provided with full-wave rectifiers V1 and V2 to vollweggleichzurichten the differential signals. Such a constructed value educational module B is shown in Figure 3a for a rotary encoder with two sample locations. The full-wave rectification is known per se, so that need not be discussed in more detail here. Obtained from the full-wave rectified difference signals U6 and U8 by combining a pulsating DC voltage G, at the level of DC voltage share of the eccentricity "e" depends.

The magnitude formation can also be computed by squaring and summing the signals U6, U8 perform. This also results in a signal whose amount of the eccentricity "e" depends.

3b shows schematically a sum educational block B4, as he would be required, for example, a not shown encoder with four sample locations.

Once in the amount education block B size has been formed, which depends on the eccentricity "e", this size is a control amplifier SV supplied with a defined response threshold, which is supplied as a reference voltage of a block R. Exceeds the size of the amount educational block B a certain value, the control amplifier SV generates a control voltage Ss which is the summation elements supplied S1 and S2. The control amplifier SV can turn in stages or work steadily.

In the summing elements S1 and S2, the scanning signals U1, U2 of the first scanning device 1 and the scanning signals U3, U4 of the second scanning device 2 is added in such a manner that for both the 0 ° -Abtastsignale U1, U3 and for the 90 ° -Abtastsignale U2, U4 sum signals U5 and U7 are formed which are weighted according to the signal (control voltage Ss) from the control amplifier SV.

The different weighting of the signals which are supplied from the sampling points A1 and A2 can be effected by an electrically controllable resistance (for example, FET or four-quadrant multiplier) whose driving voltage is supplied from the control amplifier SV in the form of the control voltage Ss.

A summing S4 for an encoder with four scanning locations A1 to A4 would be constructed as shown in Figure 4b, the skilled person to carry the circuit for multi-sample locations according to his knowledge.

In the summing elements S1, S2 so the signals U1, U3 and U2, U4 of the individual scanning points A1 and A2 are analog summed, wherein a weighting is performed by the control voltage Ss from the control amplifier SV during the addition. The proportion of the scanning of a scanning point (Hauptabtaststelle) is raised (at the same time the components of the signals of the remaining sample locations can be reduced), so that it can not come to signal cancellations. A reliable count of the sampled increments of division 5 of the graduated disk 3 is guaranteed.

The invention may also find use in linear measuring devices, for example, if material measures must be strung together to achieve the required measuring length. In these cases, multiple scanners are also provided in length measuring.

In code-measuring devices, the invention is applicable as long as the track with the highest resolution (the finest track is an incremental) is double sampled in the manner described.