Method and device for serial transmission of data between a position sensing means and a data processing unit

The invention relates to a device and a method for serial data transmission between a position measuring device and a processing unit, in particular an NC control.

Such an arrangement is known from EP-0 171 579 B1. The position measurement values ​​of the position measurement device are transmitted to this processing unit in synchronism with a clock pulse specified by a processing unit.

The main disadvantage of this arrangement is that the processing unit has to be adapted by the user to the specific parameters of the position measuring device. For example, the number of cycles required for the complete transmission of a position measurement value depends on the resolution of the position measuring device. So far, the processing unit has specified a fixed number of clock cycles (eg 13). If a position measuring device with low resolution (e.g. 5 Bit), then the 13 clock cycles are still used for measured value transmission. It can be seen that unnecessary transmission time is wasted.

DE 39 36 452 A1 discloses a method for adapting a numerical control to specific parameters of a position measuring device. The specific parameters are stored in an information carrier and transferred to the control system during a test volume.

In the. DE 41 29 577 A1 discloses a position measuring device in which a data memory with system-specific data is integrated. The outputs of the data memory and the outputs of the scanning units can be temporarily connected to transmission lines. The disadvantage here is that the synchronization between the measuring device and the evaluation unit is not guaranteed. Furthermore, the absolute value must first be generated in the processing unit, for example by arctan formation, which increases the effort in the processing unit. Another disadvantage is that multiplexers are required for transmission. The sending of parameters is only provided when the supply voltage of the measuring device is switched on. In a product description "SINCOS", edition 15.03.1993 from Stegmann, a position measuring device with a bidirectional interface and several memory areas that can be written and read about is described.

The object of the invention is therefore to optimize the adaptation of the processing unit to specific parameters of the position measuring device and to minimize the expenditure on transmission lines between the position measuring device and the processing unit.

This object is solved by the features of claim 1 and claim 7.

Advantageous refinements are specified in the dependent claims.

The particular advantages of the invention lie in the fact that the specific parameters of the position measuring device can be adopted independently by the processing unit, the same lines which are already available for the transmission of measured values ​​being used for the transmission of these parameters. Secure transmission is also guaranteed.

The invention is explained in more detail below on the basis of an exemplary embodiment shown in the drawing:

Show it:<dl id="dl0001"><dt>Figure 1</dt><dd>2 shows a basic illustration of an arrangement for serial data transmission of an angle measuring device,</dd><dt>Figure 2</dt><dd>a transmission protocol for parameter transmission,</dd><dt>Figure 3</dt><dd>schematically the sequence of the synchronous serial data transmission in a pulse-time diagram,</dd><dt>Figure 4</dt><dd>another sequence of data transmission,</dd><dt>Figure 5</dt><dd>data transmission with an interrupted clock,</dd><dt>Figure 6</dt><dd>the data transmission with a continuous cycle and</dd><dt>Figure 7</dt><dd>a circuit for bidirectional data transmission.</dd></dl>

In the exemplary embodiment shown in FIG. 1, the reference numeral 1 designates an angle measuring device which transmits the respective absolute efficiency as a binary data word (dual code) to a processing unit 4 by known photoelectrical loading of one code disk or a plurality of code disks (multitum) connected to one another via reduction gears generated by a scanning device 10 analog scanning signals which are fed to a module 2. In this module 2, the scanning signals are amplified and converted into digital signals to form a binary data word. Block 2 ensures that the complete absolute position value is always present at the output regardless of the code of the code disks. The code of the code disks can be designed as a Gray code or from several incremental tracks with a defined different division period (DE 41 25 B65 A1). Module 2 can also be used to correct the analog or digital signals. Likewise, necessary calculations are carried out in module 2 which are necessary for the correct connection or combination of several code tracks. Groups of code tracks are required. These calculations are described in detail, for example, in DE 27 58 525 B1, DE 29 38 31 8 C3 or DE 37 34 938 C2.

The absolute position measurement value is fed to a parallel-series converter 3 as an output module, which, controlled by a clock pulse sequence, sends the individual bits of the data word determining the absolute position measurement value serially to the processing unit 4 via the data line 5. It is particularly advantageous if the clock pulse sequence is specified by the processing unit 4. A clock line 6 is provided for transmitting the clock pulses from the processing unit 4 to the angle measuring device 1. The position measurement value is transmitted by means of a retriggerable time stage 7, as is explained in detail in EP 0 171 579 B1, to which express reference is made.

According to the invention, commands are also transmitted from the processing unit 4 to the position measuring device 1 via the data line 5. The commands are fed to a memory 8 of the position measuring device 1, which decodes the command and causes the position measuring device 1 to execute the corresponding command. In the example, this command is a data word consisting of three status bits S2 S1 and SO. To ensure the transmission of status commands, each status bit is also transmitted inverted, so that a total of six status bits S2, S1, S0, <maths id="math0001" num=""><math display="inline"><mrow><mover><mrow><mi mathvariant="normal">S</mi><mn>2</mn></mrow><mrow><mo>‾</mo></mrow></mover><mo>,</mo></mrow></math><img file="EP0660209B2_D0001.tif" /></maths><maths id="math0002" num=""><math display="inline"><mrow><mover><mrow><mi mathvariant="normal">S</mi><mn>1</mn></mrow><mrow><mo>‾</mo></mrow></mover><mo>,</mo></mrow></math><img file="EP0660209B2_D0002.tif" /></maths><maths id="math0003" num=""><math display="inline"><mrow><mover><mrow><mi mathvariant="normal">S</mi><mn>0</mn></mrow><mrow><mo>‾</mo></mrow></mover></mrow></math><img file="EP0660209B2_D0003.tif" /></maths>are transmitted for a command from the processing unit 4 to the position measuring device 1. If the position measuring device 1 detects a faulty status bit transmission, an error message is issued.

The position measuring device 1 is referred to below only as a measuring system.

In the example, eight status commands A to H are specified, which are described in detail below:

1. Status command A:

If the processing unit 4 sends the data word A to the position measuring device 1 via the data line 5, this means that the measuring device 1 is asked to send an absolute position measuring value to the processing unit 4. The transmission protocol for this is shown in FIGS. 3 to 6 and will be described in detail later.

2nd Status command B:

This command causes the selection of a memory area. The measuring device 1 contains a memory 9 in which parameters of the measuring device 1 can be stored. Additional memories or memory areas can be provided for correction values. It is also possible to provide an area in the memory 9 in which the user stores specific user parameters, for example motor data. It is particularly advantageous if the memory 9 is divided in such a way that the area with the parameters of the measuring system 1 can only be written by the measuring system manufacturer, and another area is freely accessible to the user (writable and readable). The area with the parameters of the measuring system manufacturer can in turn be divided into an area that can be read by the user and an area that can only be read by the measuring system manufacturer.

As can be seen in FIG. 2, the memory selection is first activated with command B to read or write parameters. After command B, a 16-bit data word (memory range select code) is sent from the processing unit 4 to the measuring system 1 in order to select an area of ​​the memory 9. The command is acknowledged by the measuring system.

3rd Status command C:

If a certain memory area is selected with command B, this command C is used to inform measuring device 1 that parameters are subsequently supplied to measuring system 1 at a specific address. This means that after this status command C, first the address information under which the parameters are to be stored and then the parameter information from the processing unit 4 are supplied to the measuring device 1 via the data line 5.

4th Status command D:

If a specific memory area is selected with command B, this command D is used to inform measuring device 1 that processing unit 4 expects the stored parameters of measuring device 1 to be sent. The processing unit 1 additionally specifies the address where these parameters are stored in the measuring device 1.

5. Status command E:

With this command E, predetermined areas of the memory 9 can be deleted at the request of the processing unit 4.

6. Status commands F to H:

These commands are advantageously reserved for testing the measuring device 1. It is thus possible, for example, for a measuring system 1 with integrated error monitoring to be tested over long distances and for the error to be diagnosed. For example, after the command F of the processing unit 4, a predetermined address of a memory area of ​​the memory 9 can be used to check whether an error message is stored there. This error message is subsequently sent from the measuring system 1 to the processing unit 4 via the data line 5.

The transmission protocol of the parameter transmission is shown in FIG. It can be seen that in the time in which the status bits, the addresses and the parameters are sent by the processing unit 4, the receiver 11 is active in the measuring system 1 and the transmitter 12 in the measuring system 1 is inactive. It can also be seen that the transmitted data for commands B and C are acknowledged by sending this data back to the processing unit 4. If it is determined in the processing unit 4 that the data sent differs from the data received, the transmission is repeated. In addition to the data, measuring system 1 also transmits an 8 bit CRC. CRC means cyclic redundancy check, this data word is obtained by a known combination of the data bits. This transmission of the CRC enables the processing unit 4 to check whether the data transmission has taken place without errors. For reasons of clarity, the inverted status bits are not shown in FIG. 2.

In Figure 1, 13 denotes the transmitter and 14 the receiver of the processing unit 4. It can also be seen that the clock 15 is accommodated in the processing unit 4. The processing unit 4 or subsequent electronics is preferably an NC control. For better understanding, two paths are shown in FIG. 1 for the data line 5. According to the invention, however, the data is transmitted bidirectionally in both directions on the same line 5, as is also shown in detail in FIG.

FIGS. 3 to 6 show pulse diagrams for the transmission of the measured position value of the measuring device 1. During the idle state, data line 5 is LOW. It can therefore be seen from the processing unit 4 that the connected position measuring device 1 is the arrangement according to the invention, since the data line is in the idle state in an arrangement according to EP 0 171 579 B1 at HIGH.

The analog values ​​of the scanning device 10 are stored in the module 2 on the first negative clock edge. When the required calculations in module 2 have been completed, which is indicated by the computing time tc, the measuring device 1 sends a start signal in the form of a start bit to the processing unit 4, in synchronism with a positive clock edge. The time tc is variable and depends on the scope of the calculations. The start bit indicates that there is a valid position measurement for transmission.

An alarm bit is transmitted after the start bit. The alarm bit reports a malfunction of the measuring device 1 to the processing unit 4. An error message is issued when an error message is stored in the memory 9. The cause of the alarm can be read from the memory 9.

With the subsequent positive clock edge, the data bits of the measured value present at the parallel-series converter 3 are transmitted serially from the transmitter 12 via the data line 5 to the processing unit 4. The length of the measured value, that is to say the necessary number of cycles, was communicated to the processing unit 4 as a parameter from the memory 9 before transmission. A CRC (cyclic redundancy check) is also transmitted to check the measured value transmission. The formation of a CRC is known from data processing.

In the exemplary embodiment according to FIG. 3, the MSB of the measured value is transmitted first and finally the LSB. In contrast, in the exemplary embodiments according to FIGS. 4 to 6, the LSB first. The inverted status bits are also shown in FIGS. 4 and 5. If the LSB is transmitted first, a fast bit-serial binary subtraction and addition during the zero point shift can be implemented without much effort during the transmission. Furthermore, this transmission has advantages in the case of code value connection calculations in accordance with DE 27 58 525 B1, DE 29 38 318 C3, DE 37 34 938 C2, since the coarser resolution code value depends on the finer resolution code value.

After a certain time tm, the measured values ​​are stored and transmitted again. The status information is again sent from the processing unit 4 to the measuring device 1 during the computing time tc.

When transmitting the position measurement, a distinction is made between an interrupted and a continuous cycle. For clarification, these two operating modes are shown in detail in FIGS. 5 and 6. The interrupted clock according to FIG. 5 is characterized in that the clock stops after the CRC transmission until a new position measurement value is stored. Before each transmission of a position measurement value to the processing unit 4, the processing unit 4 sends a status command. The interrupted cycle is particularly intended for systems which are timed, such as control loops. If a measured value is to be transmitted again in the shortest possible time, it is also possible to select the operating mode according to FIG. 6 "continuous cycle". The waiting time tm and the time for transmitting the status information are saved. The last transmitted status information is used in the processing unit 4 as current status information.

As can be seen from FIGS. 3 to 6, the processing unit 4 sends a status bit in synchronism with the falling clock edge. The status bit from measuring system 1 is accepted synchronously with the rising clock edge.

So that the arrangement for serial transmission can be used for as many measuring devices as possible, in addition to the data line 5 and clock line 6, further lines 16 are provided for the transmission of analog or binary count signals from an incremental position measuring device (FIG. 7). It is thus possible to send the count signals on the line 16 to the processing unit 4 in parallel to the absolute measured value transmission on the data line 5. It can also be seen in FIG. 7 that the bidirectional transmission of data (measured values ​​and parameters) between the measuring device 1 and the processing unit 4 takes place with signal levels according to RS485 (differential signals) in synchronism with a clock signal (CLOCK) specified by the processing unit 4. The clock frequency is between 100KHz and 2MHz.

As already mentioned, the memory 9 in the measuring device 1 enables both the customer and the manufacturer of the measuring device 1 to store and read out parameters. It is advantageous if the memory 9 is divided into several areas:<ul id="ul0001" list-style="none" compact="compact"><li>I. Storage area for customer parameters</li><li>II. Memory area for parameters of the measuring system manufacturer</li><li>III. Storage area for correction values.</li></ul>

The memory area of ​​the measuring system manufacturer is write-protected. The individual memory areas are distinguished by the code "Memory Range Select".

The memories can be used as follows:

I. Memory allocation parameters of the customer:

1. Zero shift

The value is subtracted from the zero point of measuring system 1.

II. Memory allocation parameters of the measuring system manufacturer:

These parameters can contain data that are predefined by the production, but also additional information about the operating state and operating parameters.

1. version

Specifies the version according to which the store

9 is divided.

2nd Memory size

Indication of the size of the individual areas of the memory 9.

3rd Transmission format

Indicates the number of cycles for the transmission of a measured value (data word).

4th Measuring system type

Specifies whether an incremental length or angle measuring system with or without distance-coded reference marks or whether a Singietum or Muttiturn code encoder is used.

5. Signal period or signal periods per revolution

Specifies the width of a signal period for length measuring systems or the number of signal periods per revolution for angle measuring systems.

6. Number of revolutions that can be undersigned

In the case of multiturn code angle measuring systems, the distinguishable revolutions are specified.

7. Basic distance with distance-coded reference marks or distance between two neighboring reference marks

For measuring systems with distance-coded reference marks, the basic distance of the associated reference marks is given. In measuring systems without distance-coded reference marks, the distance between two neighboring reference marks is specified.

8th. Location of the first reference mark

Indicates the position of the first reference mark in relation to the end position.

9. Measuring step or steps

For length measuring systems, specifies the measuring step that is output by the measuring system during serial data transmission. In the case of angle measuring systems, the number of measuring steps per revolution is specified.

10th Zero point shift of the measuring system

Manufacturer

11. Direction and code output for code angle measuring systems

12th ID number of the measuring system

13. Serial number of the measuring system

14. Alarms

Any errors that have occurred are saved. If, for example, a bit is not equal to zero, the alarm bit is set when measured values ​​are transmitted according to FIG. An alarm message can also be used for an emergency shutdown of a drive.

15. Warnings

If tolerance specifications for certain internal parameters of the measuring system that can lead to failure of the measuring system are exceeded, these are saved in the form of warning messages and can be read out on request. In the case of battery-operated measuring systems, a warning message can be, for example, the word "battery change °. Warnings therefore enable preventive maintenance.

III. Memory allocation correction values

<ul id="ul0002" list-style="none"><li>1. Number of correction values ​​related to the measuring length</li><li>2nd Number of correction values ​​for signal deviations such as signal amplitudes, phase shift and zero point deviations.</li><li>3rd Number of correction values ​​for harmonics.</li><li>4th Number of harmonics to be corrected.</li><li>5. Correction values ​​for 1.</li><li>6. Correction values ​​for 2.</li><li>7. Correction values ​​for 3.</li></ul>

It is of course within the scope of the invention to also make other parameters available in the memory 9 for the processing unit 4. During commissioning, the processing unit 4 is adapted by taking over the necessary parameters from the measuring system 1 via the data line 5.

The areas of the memory 9 can be divided by software, but it is also possible for the memory 9 to consist of several individual memory modules.

It is obvious that the arrangement according to the invention has the following advantages:<ul id="ul0003" list-style="dash" compact="compact"><li>Use for code measuring systems and incremental measuring systems,</li><li>Minimized transmission times for the absolute position value. For applications in a closed control loop, this reduces dead times and improves control behavior,</li><li>Bidirectional interface with the possibility of being able to save and read out parameters in the measuring system for both the customer and the measuring system manufacturer (simplification of commissioning),</li><li>Support of monitoring and diagnostic functions of the processing unit,</li><li>With absolute measuring systems, complete absolute values ​​are transmitted in the dual code regardless of the type of determination of the absolute position measured value, so that no different evaluation is required in the processing unit.</li><li>The length of the format for transmitting the position measurement value is variable and depends on the respective measuring system. The number of cycles and the assignment of the position measurement value to the cycles are determined by the content of the memory to be queried in the measuring system.</li></ul>

As can be seen from the preceding explanations, it is particularly advantageous if the clock is specified by the processing unit 4. This ensures synchronous data transmission.

However, the invention can also be used if the clock is predetermined by the measuring system 1. Here, the processing unit 4 sends a request signal (request) to the measuring system 1 via the clock line 6. The bits of the position measurement value are then sent serially to the processing unit 4 via the data line 5 in synchronism with an internal clock. In order to ensure a transmission that is synchronous with the processing cycle of the processing unit 4, the internal clock generator of the measuring system 1 can be equipped with a. Edge of the request signal can be synchronized. The request signal can also be sent to the measuring system 1 via the data line 5.

The invention can be used with angle and length measuring devices. The scanning principle is not limited to the photoelectric principle. The code for forming the position measurement value to be transmitted can be provided in a single track (chain code) or in several tracks on one or more code carriers.