Abstract:
In a method for operating a positional measurement device and a corresponding positional measurement device, the device includes a signal generation unit configured to generate positional data and is connected to sequential or follower electronics by a communication unit. Data is transmitted between the signal generation unit and the communication unit via an internal interface unit, whereas measurement-data request instructions, which are transmitted by the sequential or follower electronics to the positional measurement device, are transmitted to the signal generation unit by bypassing the internal interface unit.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for operating a position-measuring device, as well as a position-measuring device.  
       BACKGROUND INFORMATION  
       [0002]     In position-measuring devices which are used in the automation sector, data is often transmitted between the position-measuring device and a downstream sequential electronics via digital, serial interfaces. In this context, on the side of the position-measuring device, an architecture is provided such that it includes a signal-generating unit which is connected to a communication unit via an internal interface unit. The communication with the sequential electronics in turn takes place via the communication unit. For example, with the aid of the signal-generating unit, analog, position-dependent signals are generated in a conventional manner from the scanning of a suitable measuring graduation and suitably conditioned in order to be transmitted in serial form via the communication unit to the sequential electronics. The internal interface unit is provided in order to be able to flexibly combine greatly differing communication units with greatly differing signal-generating units within the framework of a modular system concept.  
         [0003]     In such an architecture, the transmission of a measurement-data request instruction from the sequential electronics to the signal-generating unit and its execution by the signal-generating unit, i.e., the actual measured-value acquisition, must be regarded as fundamentally time-critical. For example, via the measurement-data request instructions, instantaneous positional data are fetched from the position-measuring device for control purposes. To ensure high control performance on the side of the sequential electronics, it is desirable to acquire measurement data, or more precisely, positional data, in a manner as free of delay as possible.  
         [0004]     European Published Patent Application No. 0 660 209 describes a position-measuring device to which a processing unit sends commands in the form of data words transmitted in bit-serial fashion, and as a function of these commands, measured position values or parameters are requested from the position-measuring device, or parameters are sent to the position-measuring device.  
         [0005]     Furthermore, U.S. patent application Publication No. 2001/0001540 describes a position-measuring device in which, in response to a positional-data request, a measured position value is sent which is based on a measured position value that was already measured at an earlier point in time and mathematically corrected such that it corresponds to the instantaneous position value at the moment of the positional-data request. Disadvantageous in such a position-measuring device is that the accuracy of the measured position values depends upon the accuracy of the parameters needed for the correction, such as the time span between the acquisition of the measured position value and the arrival of a positional-data request, as well as the rate of change of the measured position values (e.g., traversing speed of a machine-tool axis monitored by the position-measuring device).  
       SUMMARY  
       [0006]     In accordance with example embodiments of the present invention, in a method for operating a position-measuring device and a corresponding position-measuring device, within an architecture such as that described above, it may be possible to ensure execution of a measurement-data request instruction on the side of the position-measuring device with as little delay as possible.  
         [0007]     According to an example embodiment of the present invention, e.g., with respect to the time-critical transmission to and execution of measurement-data request instructions by the signal-generating unit, it may be provided to bypass the internal interface unit of the position-measuring device and to transmit the corresponding instructions to the signal-generating unit in a manner as free of further time delay as possible. An additional signal-processing time possibly resulting in the interface unit may therefore be avoided for the time-critical measurement-data request instructions. A time-determined execution of measurement-data request instructions may be ensured.  
         [0008]     Example embodiment of the present invention may be used in conjunction with varied types of position-measuring devices, regardless of whether they are incremental or absolute position-measuring devices, and regardless of the specific scanning principle and signal-generating principle.  
         [0009]     According to an example embodiment of the present invention, a method for operating a position-measuring device connected to sequential electronics via a communication unit, the position-measuring device including a signal-generating unit configured to generate positional data, includes: (a) transmitting data between the signal-generating unit and the communication unit via an internal interface unit; (b) transmitting measurement-data request instructions, transmitted from the sequential electronics to the position-measuring device, to the signal-generating unit to immediately generate measurement data, bypassing the internal interfacing unit; and (c) transmitting the positional data, generated in accordance with the measurement-data request instructions, from the signal-generating unit to the communication unit via the internal interface unit.  
         [0010]     According to an example embodiment of the present invention, a position-measuring device, includes: a signal-generation unit configured to generate measurement data; a communication unit, the position-measuring device connected to sequential electronics via the communication unit; an internal interface configured to transmit data between the signal-generation unit and the communication unit; and a redirection device configured to transmit to the signal-generation unit measurement-data request instructions transmitted from the sequential electronics to the position-measuring device to immediately generate measurement data by bypass of the internal interface unit.  
         [0011]     According to an example embodiment of the present invention, a position-measuring device includes: signal-generating means for generating measurement data; communicating means, the position-measuring device connected to sequential electronics means via the communicating means; internal interface means for transmitting data between the signal-generating means and the communicating means; and redirection means for transmitting to the signal-generating means measurement-data request instructions transmitted from the sequential electronics means to the position-measuring device to immediately generate measurement data by bypass of the internal interface means.  
         [0012]     Further aspects and features of example embodiments of the present invention and details pertaining thereto are described below in the following description with reference to the appended Figures.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic block diagram of a position-measuring device according to an example embodiment of the present invention in conjunction with sequential electronics.  
         [0014]      FIG. 2  illustrates a position-measuring device according to an example embodiment of the present invention;  
         [0015]      FIG. 3  is a signal diagram of the time sequence of a measurement-data request when working with a position-measuring device illustrated in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  is a schematized block diagram of a position-measuring device  10  according to an example embodiment of the present invention in conjunction with sequential electronics  100 . In this context, for clarity, various components of the overall system are indicated only in highly schematic form.  
         [0017]     For example, position-measuring device  10  may be in the form of a conventional incremental or absolute position-measuring system used for determining the position of two objects movable relative to each other, for example, on a machine tool. In such an application, a numerical machine-tool control acts as sequential electronics.  
         [0018]     Data is transmitted between position-measuring device  10  and sequential electronics  100  via a data channel  50  in bidirectional, serial form. To that end, data channel  50  includes two first signal-transmission lines  51 ,  52 , indicated in schematic form, via which data is transmitted in the direction indicated by the arrows. In principle, however, data channel  50  may also be constructed differently.  
         [0019]     On the side of position-measuring device  10 , to handle the data exchange with sequential electronics  100 , a schematically indicated communication unit  12  is provided on the input side, which is responsible both for the transmission and the reception of the specific data to and from sequential electronics  100 . Communication unit  12  may be constructed differently depending on the interface physics selected or the interface protocol used. That is, example embodiments of the present invention may be used in conjunction with widely varied interface devices and, if desired, bus devices.  
         [0020]     In  FIG. 1 , communication unit  12  is indicated in schematic form as merely a single unit, but in practice may have a markedly more complex arrangement. Thus, in principle, the term communication unit should be understood to include all necessary structural elements and components on the side of the position-measuring device that may be needed for communication with the sequential electronics. In addition to interface-specific protocol components, line drivers, line receivers, transmitters, controllers, clock-data recovery modules, etc., they may include a plurality of further hardware and software elements, right up to the necessary plug-in connections, etc.  
         [0021]     To generate the actual measurement data, position-measuring device  10  also includes a signal-generating unit  11 , illustrated in schematic form. Via it, measurement data, e.g., positional data, are generated in the position-measuring device. In this context, for example, positional data may be generated from the scanning of a measuring graduation using a scanning unit that is movable relative to the measuring graduation and includes suitable scanning elements. Many different conventional arrangements come into consideration as scanning principles, thus, for example, optical, magnetic, capacitive, inductive scanning, etc., via which in each case position-dependent analog signals are able to be generated. Moreover, the generated positional data may involve widely varied types of positional data, such as, for instance, incremental positional data, absolute positional data, etc. Because of the diverse possibilities for generating the respective positional data, the signal-generating unit is only illustrated schematically in  FIG. 1 .  
         [0022]     Furthermore, signal-processing unit  15 , via which the generated—for the most part analog—measurement data or positional data are further processed, may optionally be disposed in respective position-measuring device  10 . There are also widely varied possibilities for further processing the generated positional data, depending upon the type of position-measuring device and its application. For example, it may involve signal preprocessing, signal filtering and/or signal matching before, for example, an A/D conversion and subsequent digital signal processing are also carried out. Highly diverse methods may be provided within the framework of a digital signal processing as well, for example, a signal correction, a signal interpolation, a signal monitoring, a signal diagnosis, etc. Because of these varied possibilities for signal processing, signal processing unit  15  is illustrated only schematically in  FIG. 1 . Consequently, signal processing unit  15  may also include several components.  
         [0023]     As indicated above, position-measuring device  10  also includes an internal interface unit  13 . Internal interface unit  13  is not to be understood as a physical, but rather as a logic unit which is arranged between signal-generating unit  11  and optional signal-processing unit  15  on one side and communication unit  12  on the other side. Internal interface unit  13  may be effective, e.g., with respect to a modular system arrangement, since many different variants for signal generation may be able to be flexibly combined with the different signal-transmission principles in the direction of sequential electronics  100 . In other words: widely different variants of signal-generating units  11  and, if desired, signal-processing units  15  may be flexibly combined with widely different communication units  12 , depending on the application.  
         [0024]     To that end, in a conventional manner, internal interface unit  13  may be in the form of a bidirectional interface, many different interface architectures again coming into consideration. In  FIG. 1 , this is illustrated by an addressing channel  21  and a data-transmission channel  22 .  
         [0025]     It may be provided to transmit, e.g., the time-critical measurement-data request instructions RQ, which are transmitted from sequential electronics  100  via signal-transmission line  52  of data channel  50 , to signal-generating unit  11 , while bypassing internal interface unit  13 , and to bring about their execution, i.e., the measurement-data acquisition, as promptly as possible at the signal-generating unit. As illustrated in  FIG. 1 , this is accomplished, for example, by transmitting measurement-data request instructions RQ via a separate data channel  14  in the direction of signal-generating unit  11 , thus not via internal interface unit  13  otherwise used for signal transmission in position-measuring device  10 . For example, separate data channel  14  may be in the form of a separate connecting line which bypasses internal interface unit  13 .  
         [0026]     As is apparent from the two alternative, separate data channels  14 . a ,  14 . b  illustrated in  FIG. 1 , provision may be made to send measurement-data request instructions RQ via data channel  14 . a  directly to the signal-generating unit. Alternatively, it may be possible to send measurement-data request instruction RQ via data channel  14 . b  to signal-processing unit  15 . The latter may be provided, for example, when sequential electronics  100  requests the transmission of measurement data that are derived from the actual positional data. For example, it may involve the measurement data regarding acceleration or jerk that result from the derivation of the positional data. The suitable signal processing and signal conditioning from the positional data is then carried out in signal-processing unit  15 .  
         [0027]     For the bypassing of communication unit  13  described, it may be necessary to identify measurement-data request instructions RQ in the data stream transmitted by sequential electronics  100  and to separate them. For this purpose, position-measuring device  10  and communication unit  12 , respectively, are assigned redirection units in the form of a suitable unit  16  and a separate data channel  14  which takes over this function. In the incoming data stream on signal-transmission line  52 , measurement-data request instructions RQ are identified, separated and redirected via data channel  14  in the direction of signal-generating unit  11 , bypassing internal interface unit  13 . To that end, the separated measurement-data request instructions RQ are suitably conditioned, thus permitting the desired, undelayed transmission to signal-generating unit  11 . The delay otherwise resulting in internal interface unit  13  because of the signal-processing time required there may therefore be eliminated based on the measures described herein. Prompt measured-data acquisition may be ensured on the side of position-measuring device  10 .  
         [0028]      FIG. 2  illustrates an example embodiment of a position-measuring device  10  in more detail. For reasons of clarity, communication unit  12 , as well as unit  16  which provides the redirection for measurement-data request instructions RQ, are illustrated as combined in one data-transmission unit  30 . Signal-generating unit  11  and optional signal-processing unit  15  are illustrated as combined to form one data-acquisition unit  31 . Internal interface unit  13 , which, as a logic unit, controls the data exchange between data-transmission unit  30  and data-acquisition unit  31 , is only illustrated schematically. For better understanding, identical or similar components are provided with the same reference numerals in all Figures.  
         [0029]     Data is transmitted from data-transmission unit  30  to data-acquisition unit  31  via an addressing channel  21 . In the reverse direction, thus from data-acquisition unit  31  to data-transmission unit  30 , data is transmitted via a data-transmission channel  22 .  
         [0030]     Addressing channel  21  is used for sending data request instructions and for transmitting parameters from data-transmission unit  30  to data-acquisition unit  31 . The data are transmitted synchronously with respect to the clock signal on an address clockline ADR_CLK in the form of serial data packets via n addressing lines AS 0 -AS(n- 1 ). The number n of addressing lines is arbitrary, powers of the number  2  ( 1 ,  2 ,  4 ,  8 , etc.) generally being selected in data technology. Further criteria are, for example, the complexity of the transmission protocol used, the quantity of data to be transmitted, as well as the number of available connections at the data-transmission modules. In the illustrated example embodiment, n=2 is selected.  
         [0031]     In this context, the type of data requested from data-acquisition unit  31  is not limited to positional data or measurement data. Thus, for example, the sending of error messages, warnings and diagnostic values may also be initiated. In addition, parameters which may be necessary for the operation of data-acquisition unit  31 , e.g., correction values, may be transmitted via addressing channel  21 .  
         [0032]     Data-transmission channel  22  is used for transmitting requested data from data-acquisition unit  31  to data-transmission unit  30 . For that purpose, m data lines D 0 -D(m- 1 ), as well as one data clockline DATA_CLK are provided. The number m of data lines may also be arbitrary. Similar selection criteria may be applicable as for the number n of addressing lines. In the example described, m=4.  
         [0033]     Data is transmitted on data lines DO-D(m- 1 ) synchronously with a clock signal on data clockline DATA_CLK. In this context, it may be provided that the clock signal of address clockline ADR_CLK, delayed by the signal propagation time in data-acquisition unit  31 , is used as the clock signal on data clockline DATA_CLK, since in this manner, a clock signal may easily be obtained for the synchronous data transmission, and therefore it may not be necessary to generate a separate clock signal in data acquisition unit  31 . The delay between the clock signal of address clockline ADR_CLK and the clock signal on data clockline DATA_CLK may be very small, and in  FIG. 3 , is only illustrated by point of time t 1 ′, which corresponds to point of time t 1  delayed by the signal propagation time.  
         [0034]     As described above, measurement-data request instructions RQ are identified from the data stream transmitted by sequential electronics  100 , separated and conducted via separate data channel  14  to data-acquisition unit  31 . The time gain resulting from this arrangement is illustrated in  FIG. 3 .  
         [0035]      FIG. 3  illustrates a signal diagram of the time sequence of a measurement-data request. First, at point of time t 0 , a falling edge on separate data channel  14  signals to data-acquisition unit  31  a measurement-data request instruction RQ, and the measurement-data acquisition is started without further time delay. Only after a certain time, which is a function of the processing time in data-transmission unit  30 , is a clock signal started on address clockline ADR_CLK at point of time t 1 . As of point of time t 2 , a serial data packet having the information about the type of requested data is transmitted from data-transmission unit  30  to data-acquisition unit  31  via lines AS 0  and AS 1  synchronously with the clock signal on address clockline ADR_CLK.  
         [0036]     Since when working with a position-measuring device without the redirection measures as described herein, point of time t 1  is the earliest point of time at which a measurement-data acquisition may be started, the time gain of the position-measuring device is calculated from the difference between t 1  and t 0 .  
         [0037]     When the requested data is ready in data-acquisition unit  31  at point of time t 3 , the transmission to data-transmission unit  30  begins via data lines D 0 -D 3  in the form of a serial data packet. Without the measures as described herein, point of time t 3  may be delayed by the difference between t 1  and t 0 , i.e., the transmission of data could only begin perceptibly later. As already described, the transmission proceeds synchronously with respect to the clock signal on data clockline DATA_CLK. When the data transmission is ended at point of time t 4 , a rising edge on separate data channel  14  signals that measurement-data request instruction RQ is executed. At the end of the data transmission, the clock signals on address clockline ADR_CLK and data clockline DATA_CLK are also stopped.  
         [0038]     The structure of the serial data packets may be a matter of choice. For example, in addition to the data that is actually to be transmitted, they may also include information concerning the contents and size of the data packet, status information or checksums.  
         [0039]     Since the communication between data-acquisition unit  31  and data-transmission unit  30  proceeds on two separate data channels, it is possible to request further data even before the end of the data transmission.  
         [0040]     Besides the exemplary embodiments described above, there are other alternative example embodiments within the scope hereof.