DE8915310U1 - Position measuring device with subdivision circuit - Google Patents

Description

• a ·

DR. JOHANNES HEIDENHAIN GmbH 27 November 1987 Positioning device with subdivision SS S SS SSSSiirSS SS SS SSS S SSS ST^T—.S SS S S SS SSSS S S S = SS S

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

) Incremental measuring systems, from which the invention is based, are known to deliver pulses, the number of which represents a measure of the linear displacement or the angle of rotation. These pulses are summed up as path elements in an electronic up/down counter and the measured value is displayed numerically.

The resolution of incremental position measuring devices without further electronic subdivision is initially only 1/4 of the division period, since the photodetectors of the scanning unit generate two signals U1 and U2 that are phase-shifted by 90° to each other and have four zero crossings to generate counting pulses. If the

If both signals have a sufficiently good sinusoidal shape, they can be shifted between the zero crossings to
&egr; interpolate electrically in a similar manner.

£ 5 For the following example, CH-PS 407 569

.called.

One possibility is to create additional auxiliary phases in a resistance network. The mathematical basis for this is the additive resistor. If the amplitudes of the two signals are selected

U1 = A1 sin
and
U2 = A2 cos

where P = signal period

that A1 = cos J
and

A2 = sinjf ,

Adding the two signals results in a new signal 25

ü a sin <y+ 2 7&Ggr;&KHgr;/&Rgr;)

which is phase-shifted to U1 umi . X is the path or angle and f is an auxiliary quantity which is selected according to the required degree of interpolation.

j In modern evaluation electronics, these

I X Up to 25 times phase-shifted signals can be

ti ·· I *··&Igr;&Igr;·** f < I · · ·· t ItI

and thus achieves resolutions of the measuring system of up to 1/100 of the scale division period.

However, for such high subdivisions, the circuit complexity is already quite high, since a switching module must be provided for each phase-shifted signal. So far, the number of triggers has always had to be twice the subdivision factor.

&lgr; The invention is therefore based on the object of improving a position measuring device of the type mentioned at the beginning so that the circuit complexity is not proportional to the subdivision factor. tor increases.

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

The particular advantages are that the switching modules can be used multiple times, so that a considerably smaller number of triggers is sufficient.

The invention will be explained in more detail below with the aid of exemplary embodiments and with reference to the drawings.

Figure 1 shows a schematic diagram; Figure 2 is a block diagram with two

trigger;

Figure 3 is a block diagram with two trigger groups;

Figure 4 is a block diagram with three trigger groups;

Tigur 5 a block diagram with three

Trigger groups and control logic;

Figure 6 is a signal diagram;

Figure 7 shows another signal diagram;

Figure 8 is a block diagram with two sampling points.

The basic circuit diagram in Figure 1 shows a position measuring device M, which has a measuring body 1 and a scanning device 2. The measuring body 1 and the scanning device 2 are each attached to one of two unspecified machine components whose relative movement is to be measured. When the machine components move relative to each other, the scanning device 2 generates analog scanning signals U1, U2, which are approximately sinusoidal, by scanning the measuring body 1 in a known manner. To detect the direction of movement, the scanning signals U1, U2 are phase-shifted by 90° from each other. In everyday language, terms such as sine signal and cosine signal or even 0° and 90" signal have therefore become established.

The sampling signals U1, U2 are fed into an analog signal processing circuit A. There, a signal period P of the sampling signals U1, U2 is broken down into a number of sectors P1, P2, P3, P4. The number of sectors Pn depends on the desired

Degree of subdivision and the circuit components/ which are subordinate to the analog signal processing circuit A. The sectors P1, P2, P3, P4 are limited by their associated edge signals. 5

In the case of the example in Figure 1, each sector covers an area of Tf/2, so that we can speak of quadrants here, which thus represent a special form of sector division.

A switching module 3, which is controlled by a control circuit 4, is connected to both the analog signal processing circuit A and to a comparator T. In the comparator T there is at least one trigger module. However, since the analog signals U1, U2 are to be divided as high as possible, in practice several trigger modules are implemented as trigger groups in the comparator T. These cases will be discussed in more detail using the following figures.

Depending on control signals fed to it by the control circuit 4, the switching module 3 switches the comparator T to the individual sectors P1, P2, P3, P4 in a predeterminable sequence. The signals of the individual sectors P1, P2, P3, P4 are thus triggered one after the other by the comparator T, so that square-wave signal sequences of the desired frequency are present at the output of the comparator T, which are also phase-shifted by 90° from one another.

Figure 2 shows a block diagram in which a comparator T2 consists of two triggers T12 and T22. A switching module 32 is formed by two so-called analog multiplexers 312 and 322. A

Control circuit 42 has an evaluation logic 412, a clocked up-down counter 422 and a converter module 432, by means of which the control signals for switching the analog multiplexers 312 and 322 are obtained from the counter reading of the up-down counter 422.

From the analog ⁰ ° and 90° scanning signals U1, U2, two groups of ten signals each, 0° to 162° and 9° to 171°, are formed in the analog signal processing circuit A2, which are phase-shifted by 18° from one another. In this way, ten sectors with a width of (electrically) 18° are formed for each analog scanning signal U1 and U2.

¹⁵

The first group of analog signals to be triggered, which were formed from the sampling signal U1, is applied to the first analog multiplexer 312; the second group of analog signals, formed from the sampling signal U2, is applied to the second analog multiplexer 322.

The example shows how the analog signals are distributed to the analog multiplexers 312 and 322.

The 0"^ signal is present at the 1st stage of the 1st analog

9 "-Signal" &eegr;&eegr; 1 . " 2. multiplexers The 18 "-Signal" &eegr;&pgr; 2. " 1 . The The 27 "-Signal" &bull;&igr;&eegr; 2. " 2. It The 36 "-Signal" &eegr;&eegr; 3. " 1. &eegr; 30 The 45 "-Signal" Il It 3. " 2. &eegr; The .W. H U,S

Each analog multiplexer 312 and 322 has an output

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to which a trigger T12 and T22 is connected.

The two triggers T12 and T22 are always connected to two adjacent input signals, whereby the trigger T12 is always connected to the input signal that

smaller phase shift, coupled |

. is. The position of the analog multiplexers 312, 322 k

is the zero crossing of the input signals with

Using the running up-down counter 422 ,

tracked. When the position measuring unit is at a standstill, ;,'

direction, the two triggers T12, T22, S outside the zero crossings of the O° signal, provide the state 1

Ü 0 and 1. If trigger T12 changes the state, this means a backward movement. The up-down counter 422 jumps back one step. If trigger T22 changes the state, a forward step must be carried out. The 0° and 90° square wave output signals are obtained from the counter reading.

In the embodiment shown in Figure 3, the division period P of the sampling signals U1, U2 is broken down into sectors in the analog signal processing circuit A3 in the manner described above. The edge signals of a sector Pi are each connected to one of the trigger groups T13 or T23, which divides the relevant sector Pi and detects the zero crossings. The coupling of the respective sector || edge signals to the relevant trigger group T13 I ¹

or T23 is done by means of an analog circuit module 33. The EXE3 circuit uses two trigger groups T13 and T23 which are alternately placed in advance on the next current sector Pi + 1. The assignment of sector Pi and trigger group T13 or T23 depends on the position of the switches in the analog circuit module 33, which is controlled by a control circuit.

fltMf·*!·

tung 43 receives the switching commands. The control circuit 43 contains an evaluation logic 413, a clocked up-down counter 423 and a converter module 433, by means of which the control signals for switching the analog circuit module 33 are obtained from the counter reading of the up-down counter 423.

If the position measuring device M runs through a division period P, the up-down counter 423 must be precisely tracked, as it in turn ensures that the correct trigger group Ti is connected to the correct sector Pl via the analog switching module 33. The up-down counter 423 is tracked by releasing a forward pulse or by releasing a backward pulse. The decision as to whether and which release should occur is taken from a table stored in the evaluation logic 413. This table has as input information the status of the up-down counter 423 and the status of the triggers of the current trigger group T13 or T23.

At a certain level of the up-down counter 423, there is only one valid status image of the trigger groups T13, T23 for a forward pulse and only one status image for a backward pulse. When such an input combination occurs, the up-down counter 423 is enabled in one direction or the other. Once the up-down counter 423 has carried out this counting step, the input information of the decision table also changes and the enable disappears again. The table can be implemented as a memory module. In order to

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To synchronize counter 423 at start-up, it is set to zero when a complete division period is completed.

A further embodiment is shown in Figure 4. There, the control signals for controlling an analog switching module 34 are supplied by a control circuit 44 which has an external logic 414, a further trigger IC group T34 and a converter module 424.

The comparator T4 can contain one or more trigger groups T14, T24. The following explanations refer to two trigger groups T14, T24.

The phase-shifted signals U1, U2 of a division period P are again divided into sectors P1 to Pn is broken down. The edge signals of a sector Pi are each connected to a trigger group T14 or T24, which divides the sector Pi and detects the zero crossings. Connecting the sector edge signals and the trigger group T14 or T24 is done with the analog switching module 34. The circuit EXE4 uses two switchable trigger groups T14 to T24. They are placed alternately, looking ahead, to the next current sector Pi + 1.

The position of the analog switching module 34 is determined by the output signals of the third trigger group* T34. This trigger group T34 is connected to the phase-shifted input signals at U1, U2, -U1 and is not switched.

The switchable trigger groups T14, T24 are each assigned to certain sectors Pi. If the input signal U1, U2 coming from the position measuring device M has passed through the middle of the sector Pi, the group T14 or &idigr;:24 that is not currently being used is switched over. This is placed on the sector Pi + I, which, while maintaining the direction of movement, will be passed through next. The sector center is detected by the rigid trigger group T34. The output signals of the trigger groups T14, T24, T34 are fed to an evaluation logic 414.

The evaluation logic 414 contains a signal lock and a code converter. The lock prevents the pulses resulting from the trigger group switching from affecting the output. The code converter generates the 0° and 90° square-wave output signals. 20

A similar circuit is shown as EXE5 in Figure 5. Sectors P1 to Pn are formed from analog sampling signals U1 , U2 in an analog signal conditioning circuit A5. 25

The edge signals of a sector Pi are each switched to a trigger group T15 or T25, which the sector Pi and the zero crossings

detected.

^ 30

The connection of the sector edge signals and the trigger group T15 or T25 is done with an analog switch.

µm block 35. The EXE5 circuit uses two

switchable trigger groups T15 and T25. They are

# · * ti t t Il · I

&bull; · * fill I · t ·

&bull; · ·■ · I · ff«

&bull; * · ·» I I I 1 ti II· Il

- 15 -

alternately, looking ahead, placed on the next current sector Pl + 1.

The position of the analog switching module 35 is determined by the output signals of another/rigid trigger group T35 and the output signals of the switchable trigger groups T15 and T25. The rigid trigger group T3b is permanently connected to the phase-shifted input signals U1, U2.

The switchable trigger groups T15 or T25 are each assigned to certain sectors Pi or Pi + 1. If the input signal coming from the encoder has passed through the middle of a sector Pi, the trigger group T15 or T25 that is not currently being used is switched. This is placed on the sector Pi + 1, which is the next sector to be passed through if the direction of movement is maintained. The sector center is detected by the rigid and the switchable triggers T15, T25, T35.

These trigger output signals are fed to a control circuit 45, which determines the position of the analog switching module 35.

The control circuit 45 contains, in addition to the actual switching logic 435, an evaluation logic 415, a start logic 425 and the third trigger group T35 already mentioned.

The evaluation logic 415 for generating the square-wave output signals also uses all trigger signals. It consists of a filter for the switching pulses (not described in detail) and a

if not described in more detail, a code converter stage for conversion into the 0 ^ö and 90° square wave output signals. The described functional principle requires a special start logic 425. 5

If the analog switching module 35 is in an invalid position after switching on, an appropriate response must be made. The invalid switch position is recognized by the fact that the output states of all switchable trigger groups T15 and T25 are at ONE or ZERO.

A signal diagram/ in which one of the sampling signals U1 and its subdivision is shown is shown in Figure 6. There are two trigger groups T1 and T2, each of which has five triggers 1 ¹ to 5 ¹ and 6 ¹ to 10'. In this case, a signal period P is divided into eight sectors P1 to P8 and each sector Pi is further divided by one of the two trigger groups T1 or T2, each with five triggers 1 ¹ to 5' and 6 ¹ to 10'. Inverting triggers were assumed for the trigger modules.

In Figure 7, the analog signal switching is shown in three partial sketches a, b and c. Figure 7a shows the two sampling signals U1 and U2, which are phase-shifted by 90° to each other.

By switching the phase-shifted sampling signals U1, U2 in an EXE with analog signal switching, the harmonic component of the input voltage of the trigger stages increases, see Figure 7b·

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By switching to the inverted, phase-shifted input signals, the harmonic content of the input voltage can be reduced.

For an EXE with four sectors, the inverted input signals must be switched between and 243°, see Figure 7c.

If the inversion is carried out in the analog part of the circuit, it can be saved in the digital evaluation logic.

The circuit principle - using only a few comparators Ti in a subdivision circuit EXE and switching these alternately to different sectors of the scanning signals U1, U2 - can also be used very advantageously in position measuring devices that have several scanning points ASI to ASn.

This is explained using the block diagram in Figure 8. Since the division principle is essentially the same as the previous examples, only the special features will be discussed in more detail.

An angle measuring device (not shown) has two diametrical sampling points ASI and ASU to compensate for the eccentricity, each sampling point ASI and ASU delivers 0° and 90° signals U1, U2 and U3, U4. To ensure that the subdivision effort is not doubled by the double number of sampling points ASI and ASU, the analog sampling signals U1, U2 and U3, U4 are stored in so-called "sample & hold" memories SH1, SH2, SH3 and SH4

buffered. By means of a memory control circuit A4, the buffered analog sampling signals U1, U2 or U3, U4 are fed to a sampling point ASI or ASU one after the other to an analog processing circuit AS, whereby the memories SH1, SH2 or SH3, SH4 are connected one after the other to the analog signal processing circuit A8, so that the respective memory contents can be transferred sampling point by sampling point.

An analog switching module 38 switches a com-

' parator (T8), which consists of one or more trig

can happily exist, to the various sectors,

which, in a similar manner as already described, are formed in the analog signal processing circuit A8 from the sampling signals U1, U2 or U3, U4 of a sampling point ASI or ASU. After triggering the again sub-

divided sector signals, these square-wave signals, which are phase-shifted relative to one another, are stored in digital memories L1 and L2. The digital memory L1 stores the binary values of the sampling point ASI and the digital memory L2 stores the binary

values of the sampling point ASU are stored.

The memory control circuit A4 ensures that

Ä the analog sampling signals Ü3, U4 of the second

l_ button ASU only then in the analog signal

30 conditioning circuit A8 can be processed,

when the sampling signals U1, U2 of the first sampling

P stelle ASI completely divided, digitized

J| and stored in the associated digital memory L1

S are.

- 19 -

After the division process for the signals of the last sampling point - here the signals Ü3, U4 of the sampling point ASU - has been completed with the storage of the binary values in the digital memory L2, the binary values of all sampling points ASI and ASXI are added in an addition stage, which is formed by a full adder V, and divided by the number of sampling points, in this case two.

Claims (1)

DR. JOHANNES HEIDENHAIN GmbH 27 November 1987 Sayings 1. Position measuring device (M) for determining an angle or path (Xi) with a subdivision circuit (EXEi) for analog scanning signals (171, U2) which are generated by scanning a M&IvesccToerung '1) by means of a scanning device (2j), in which the sub-division (3EDC?i) has at least one comparator (Ti) _t characterized in that the scanning signals (U 1, U2) of an analog log signal processing circuit (Ai) that in the analog signal processing circuit (Ai) a signal period (P) of the scanning signals (U1, U2) is divided into a predeterminable number of sectors (P1 to Pn) and that between the analog signal processing circuit (Ai) and the at least one comparator (Ti) a switching module (3i) is provided, which, depending on control signals from a control circuit (4i), rator (Ti) successively assigns the individual sectors (P1 to Pn) and divides them. 2. Position measuring device according to claim 1, characterized in that two triggers (T12, T22) are provided as comparator (T2) and two analog multiplexers (312 and 322) are provided as switching module (32), and that the triggers (T12, T22) are connected in sections with the aid of the analog multiplexers (312, 322). III * « depending on control signals of a control circuit (42) are successively assigned to the individual sectors (Pi). 5 3. Position measuring device according to claim 1, characterized in that two trigger groups (T13, T23 _f T14, T24, T15, 725) are provided as comparator (T3, T4, T5) and an analog switch (33, 34, 35) is provided as switching module 10, and that the trigger groups (T13, ""23, T14, T24, T15, T25) with the aid of the analog switch (33, 24, 35) depending on control signals of a control circuit (43, 44, 45) alternately looking ahead to the next 15 current sector (Pi +1). 4. Position measuring device according to claim 2, characterized in that the control circuit I (42) comprises an evaluation logic (412), a clocked I 20 th up-down counter (422) and a wall § ler module (432) which is connected to the analog t] multiplexer (312, 322) and I depending on the status of the front-back 1 down counter (422). ^S25 j4 5. Position measuring device according to claim 3, : characterized in that the control circuit ij (43) an evaluation logic (413), a clocked I th up-down counter (423) and a converter module (433) which is connected to the analog . ⁽ switch (33) is connected and it is in ■i Dependence on the status of the up-down counter - (423) switches. # 6. Position measuring device according to claim 5, characterized in that the status of the forward-backward counter (423) is dependent on input information at the evaluation logic (413) which is derived from the status of the forward-backward counter (423) and the states of the trigger groups (T13, T23). &Iacgr;. Dnol flnnainoSoinr iehtvino after Ancnruch 3. da &mdash; characterized in that the control circuit (44, 45) has an evaluation logic (414, 415), a third trigger group (T34, T35) and a converter module (434, 435) which is connected to the analog switch (34, 35), and switches it depending on output signals of the third trigger group (T34, T35) to which the sampling signals (U1, U2) are fed. 8. Position measuring device according to claim 1, characterized in that the signals of the sectors (P1 to Pn) obtained from the scanning signals (UI , Ü2) are inverted in the analog signal processing circuit (A). 9. Position measuring device according to claim 1, wherein at least two sampling points (ASI, ASU) are provided for scanning the measurement embodiment (1), characterized in that the analog sampling signals (U1 to Un) are temporarily stored in memories (SHI to SH4) and that with the help of a memory control circuit (A4) the sampling signals (Ü1 to Un) are sent one after the other to the analog signal processing circuit ·■ ·< ft · · ·· <■ ■ y\ (A8) and then divided. 10. Position measuring device according to claim 9, characterized in that the divided signals of each sampling point (ASI, ASU) are digitized one after the other and stored in a data memory (L1, L2). 11. Position measuring device according to claim 10, characterized in that the digitized values of all sampling points (ASI, ASU) are averaged. 12. Position measuring device according to claim 11, characterized in that an addition stage (V) is provided for averaging the digitized values, in which the digitized values of all sampling points (ASI, ASU) are first added and then divided by the number of sampling points.