Absolute position-measuring device

A position-measuring device includes: a first subassembly having a measuring standard on which at least one coded track is provided, and a scanning unit, which is able to generate position signals that may be used to generate an absolute digital position value by scanning the at least one coded track in a measuring direction; a second subassembly having at least one peripheral unit adapted to execute a supplementary or an auxiliary functionality of the position-measuring device; and a plurality of electrical lines, which connect the first subassembly and the second subassembly to each other for the transmission of electrical signals. The position-measuring device is able to be operated in an initialization mode and in a standard operating mode. All components of the first subassembly required for the operation in the standard operating mode are components that are suitable for use in a radiation region of a machine. Furthermore, an initialization memory is provided in the first subassembly, which includes the data required for the operation in the standard operating mode and which is not suitable for use in a radiation region of a machine. In the initialization mode, the content of the initialization memory is transmittable to a memory unit situated outside the radiation region. Only the content of the memory unit is used for the operation in the standard operating mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Application No. 10 2013 219 099.9, filed in the Federal Republic of Germany on Sep. 24, 2013, which is expressly incorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to an absolute position-measuring device, and to a method for operating a position-measuring device. Absolute position-measuring devices, as described herein, are suitable for use in systems or machines in which it is exposed to high-energy ionizing radiation.

BACKGROUND INFORMATION

Position-measuring devices are required in a wide variety of technical fields in order to determine the position (length and/or angle) of movable components in systems and machines. Based on their functional principle, position-measuring devices of this type are subdivided into two groups. There are, for example, incremental position-measuring devices, in which the position is determined by counting graduation periods of an incremental graduation. There are also absolute position-measuring devices, in which the position is obtained by scanning and analyzing an absolute graduation.

In contrast to absolute position-measuring devices, incremental position-measuring devices have a simple, robust design, but the drawback that no positional information is available directly following the switch-on operation, and it is necessary to first cross a reference mark in a so-called reference run before the absolute position can be inferred. For this reason, absolute position-measuring devices, in which an absolute position value is available at all times, also immediately after the device is switched on, have since become the preferred choice in many technical fields. An absolute position-measuring device is described, for example, in European Published Patent Application No. 0 660 209.

A technical field in which the use of absolute position-measuring devices continues to be problematic concerns systems or machines that are exposed to ionizing high-energy radiation, or whose application field requires the use of such radiation. Especially the field of medical technology should be mentioned in this context, where ionizing high-energy radiation is selectively used to treat diseases or to delay their progression. Gamma radiation, X-ray radiation or particle radiation (protons, neutrons, electrons etc.) are predominantly used in this regard.

Incremental position-measuring devices that are exposed to such radiation exhibit a fairly robust response due to their simple design. On the other hand, absolute position-measuring devices, which require a more complex design to determine an absolute positional value, tend to fail when exposed to ionizing, high-energy radiation. Memory components are especially problematic, since memory content may change under the influence of radiation. The failures caused by this problem are frequently difficult to understand because of the inconsistent error images they create.

German Published Patent Application No. 10 2012 218 890 describes an absolute position-measuring device, which may be suitable for use in an environment in which it may be exposed to ionizing high-energy radiation. It includes two subassemblies, in which a first subassembly includes functional blocks used directly for a position measurement, and a second subassembly including functional blocks that perform auxiliary and supplementary functions. The first subassembly is completely made up of so-called radiation-hardened components, e.g., components that are suitable for use in a radiation region of a machine. Because the second subassembly can be situated in a separate location from the first subassembly and thus outside the radiation region of the machine, the second subassembly may be made up of conventional components. This separation of the functions of the position-measuring device provides a favorable cost/benefit ratio.

This also applies to the service case, because the exchange of one of the subassemblies may possibly be sufficient. In practice, the subassembly to be exchanged will frequently involve the first subassembly, not only because it is operated in the environment of ionizing high-energy radiation, but also because this subassembly is exposed to mechanical wear, temperature fluctuations, etc.

The manufacturer frequently assigns data to the first subassembly that are required for operating the position-measuring device. The data may involve information regarding the technical specifications (resolution, interface protocol, type designation, etc.), which are also referred to as electronic nameplates. In addition, these data may include calibration values required to optimize the accuracy of the position-measuring device. Since the use of memory components is problematic for the aforementioned reasons, the manufacturer of the position-measuring device or the first subassembly must supply these data separately from the device, e.g., stored on a data carrier (DVD-ROM, CD-ROM, etc.) or in the form of a hard copy.

A service technician handling the exchange of the first subassembly must then also copy the supplied data to the location where they are required for operating the position-measuring device, e.g., either into the second subassembly (where memory chips may be used because it is operated outside the radiation region of the machine), or into the sequential electronics to which the position-measuring device is connected (e.g., a numerical control). However, this procedure is undesired because it is complicated and prone to errors.

SUMMARY

Example embodiments of the present invention provide a absolute position-measuring device that is easy to service, and example embodiments of the present invention provide a method for the safe initialization of such a position-measuring device.

According to example embodiments of the present invention, an absolute position-measuring device includes: a first subassembly having a measuring standard on which at least one coded track is arranged, and a scanning unit, which is able to generate position signals that may be used to generate an absolute digital position value by scanning the at least one coded track in a measuring direction; a second subassembly having at least one peripheral unit, which is adapted to execute a supplementary or an auxiliary functionality of the position-measuring device; and a plurality of electrical lines, which connect the first subassembly and the second subassembly to each other for the transmission of electrical signals. It is possible to operate the position-measuring device in an initialization mode and in a standard operating mode, and all components of the first subassembly required for the operation in the standard operating mode are components that are suitable for use in a radiation region of a machine. Furthermore, an initialization memory is provided in the first subassembly, which includes data required for the operation in the standard operating mode and which is not suitable for use in a radiation region of a machine and in the initialization mode, the content of the initialization memory being transmittable to a memory unit that is disposed outside the radiation region and the content of the memory unit being used for the operation in the standard operating mode.

According to example embodiments of the present invention, a method is provided for operating an absolute position-measuring device. A first subassembly includes a measuring standard on which at least one coded track is arranged, and a scanning unit, which is able to generate position signals that can be used to generate an absolute digital positional value by scanning the at least one coded track in a measuring direction. A second subassembly includes at least one peripheral unit, which is adapted to execute a supplementary or an auxiliary functionality of the position-measuring device, and a plurality of electrical lines connect the first subassembly and the second subassembly to each other for the transmission of electrical signals. It is possible to operate the position-measuring device in an initialization mode and a standard operating mode, and all components of the first subassembly required for the operation in the standard operating mode are components that are suitable for use in a radiation region of a machine. Furthermore, an initialization memory is provided in the first subassembly, which includes data required for the operation in the standard operating mode and which is not suitable for use in a radiation region of a machine. According to the method, in the initialization mode, the content of the initialization memory is transmitted to a memory unit that is arranged outside the radiation region, and the content of the memory unit is used for the operation in the standard operating mode.

DETAILED DESCRIPTION

FIG. 1ais a schematic plan view andFIG. 1bis a schematic side view of a medical radiation device1as examples of a system in which ionizing high-energy radiation is used, especially gamma radiation, x-ray radiation or electron radiation. A radiation source2of radiation device1is arranged above the illustrated head end of a patient examination table3. For clarity, a detailed depiction of the radiation source is omitted. It should be understood that the ionizing, high-energy radiation used for the radiation treatment of a tumor, for example, may occur predominantly within circle10illustrated inFIG. 1a. The area within circle10is therefore referred to below as radiation region A. Outside radiation region A, and thus outside circle10, there is a radiation-proof region B.

The foregoing subdivision is greatly simplified and is mainly used for illustrative purposes. In practice, the energy of the occurring radiation decreases with rising distance from the radiation source, so that no exact boundary line can be drawn. For the following discussion, radiation region A means the region of a system in which ionizing, high-energy radiation may occur at a dose that could have an adverse effect on the functional reliability of a conventional absolute position-measuring device. On the other hand, a radiation-proof region B describes the area around a system in which the functional reliability of conventional absolute position-measuring devices is not affected by the occurring radiation.

In addition to maintaining a certain minimum distance from the radiation source, a radiation-proof region B may also be created by introducing a shielding barrier in the propagation direction of the radiation. Lead, for example, is a particularly suitable material for this purpose.

Two robot arms5and6are provided on the medical radiation device, the first robot arm5supporting a transmitter unit7, and the second robot arm6supporting a receiver unit8of a computer tomograph (CT). Robot arms5,6are used for the precise positioning of transmitter unit7and receiver unit8with the aid of servomotors, their position being determined by position-measuring devices20, e.g. rotary transducers or angle-measuring devices disposed in the joints of robot arms5,6.

The patient examination table is movable in the direction of the illustrated arrow, and its position is measured with the aid of a further position-measuring device20, e.g., a linear measuring device.

In some instances, such medical radiation devices already use radiation energy of more than 20 MeV. As a result, a considerable radiation dose may be introduced into position-measuring devices20over the service life of such a device. The used radiation may be gamma radiation, x-ray radiation or particle radiation (protons, neurons, electrons, etc.).

FIG. 2is a block diagram of a position-measuring device20according to an example embodiment of the present invention, which is suitable for use in a system in which position-measuring device20may be exposed to ionizing, high-energy radiation. Position-measuring device20includes a first subassembly20.1and a second subassembly20.2. To transmit electrical signals between first subassembly20.1and second subassembly20.2, the subassemblies are interconnected via a plurality of electrical lines21. First subassembly20.1is used in radiation region A (to the left of the perpendicular dashed line inFIG. 2), and second subassembly20.2is used in the radiation-proof region B of a machine or system.

To generate position signals S that are able to be processed into an absolute position value P, first subassembly20.1includes a measuring standard22having at least one coded track23, as well as a scanning unit24for scanning the at least one coded track23. Coded track23may be encoded in a parallel manner (e. g., Gray code) or, as illustrated inFIG. 2, in a serial manner (Pseudo Random Code PRC). However, the encoding may also be implemented in an analog manner, such as by multiple parallel coded tracks23that have a different graduation period (Vernier principle). Measuring standard22and scanning unit24are disposed in a manner allowing movement relative to each other in a measuring direction X.

If position-measuring device20is arranged as a linear measuring device, then measuring standard22, for example, is a scale on which coded track23is applied. In a rotary transducer or angle-measuring device, measuring standard22is usually implemented as circular disk, and coded track23is disposed in the form of a ring around the center of the disk.

In this exemplary embodiment, it is assumed that position-measuring device20is operating according to the optical transmitted-light principle, e.g., the positional information of coded track23is encoded by a sequence of transparent and opaque regions, and scanning unit24includes a light source25provided on one side of measuring standard22, which radiates light in the direction of coded track23, and a detector unit26, which generates position signals S from the light modulated by coded track23. Position signals S may be present both in analog and digital form and are suitable as basis for generating an absolute digital position value P.

In addition to the optical scanning principle, other scanning principles are usable as well, especially magnetic, capacitive or inductive principles. In the same manner, it is possible to use an optical incident light principle, in which coded track23is made up of reflective and non-reflective regions and light source25and detector unit26are therefore provided on a side of measuring standard22.

An initialization memory70may be provided in first subassembly20.1. It includes data that are relevant for the operation of position-measuring device20, such as information in connection with technical specifications (resolution, interface protocol, type designation, etc.) or calibration values. Initialization memory70is programmed by the manufacturer of position-measuring device20, specifically the manufacturer of first subassembly20.1, and its content can be read out via an interface38. Because the data relevant for the operation are also always supplied in the service case when first subassembly20.1needs to be exchanged, the renewed startup of position-measuring device20is able to be simplified, as shown below, such that configuration errors are virtually impossible.

Second subassembly20.2includes peripheral units of position-measuring device20that perform supplementary or auxiliary functions. For example, second subassembly20.2may include a communications unit30, a signal-processing unit31, a reset unit32, a voltage-supply unit33, and a memory unit34.

At least a few of the peripheral units (in this exemplary embodiment, communications unit30, signal-processing unit31, and memory unit34) as well as scanning unit24or detector unit26in first subassembly20.1have an internal interface38. The interface of initialization memory70is likewise an internal interface38. In addition, scanning unit24may include an internal interface38. All internal interfaces38are interconnected via suitable signal lines. Internal interfaces38provide the physical prerequisites for a communication and are suitably adapted for the transmission of data according to the rules of an interface protocol. The data transmission may be carried out in a parallel or serial manner.

On the one side, communications unit30provides a digital device interface36, via which the communication with a control unit50takes place, at which position-measuring device20is operated. Device interface36, for one, includes the physical preconditions for the communication (signal level, data rate, plug connector, etc.) and, for another, it includes a communications protocol that specifies the communication rules between position-measuring device20and control unit50. Device interface36may be arranged as a serial, e.g., synchronous-serial, interface, and the signals are transmitted differentially, in a conventional manner, such as according to the RS-485 standard. Second subassembly20.2and control unit50are interconnected via a suitable data transmission cable52.

As mentioned above, on the other side, communication unit30provides an internal interface38that is suitable for communicating with peripheral units of second subassembly20.2(in the illustrated example, with signal-processing unit31and memory unit34) and with first subassembly20.1, especially also to read out initialization memory70. Since it is advantageous if the communication is controlled by communications unit30, internal interface38of communications unit30is preferably implemented as a so-called master interface, and internal interface38of the further components is arranged as a slave interface. The interface connection control unit50—device interface36—internal interface36also allows control unit50to access components provided with an internal interface38. In particular, this interface connection may be used to read and possibly program memory contents of initialization memory70and memory unit34.

Signal-processing unit31generates a digital absolute position value P from position signals S that are supplied to second subassembly20.2by first subassembly20.1via electrical lines21, and transmits this value, possibly in response to a position request command of control unit50, to communications unit30via internal interface38. Toward this end, the functions of signal-processing unit31may include an analog-digital conversion, a detection of faulty position signals S, the selection of valid signals from a number of redundant position signals S, etc.

The function of reset unit32, for example, may include monitoring the supply voltage of position-measuring device20and outputting a reset signal in the event of fluctuations of the supply voltage, in order to prevent undefined operating states. Among other things, reset unit32also ensures that a normal operation following the switch-on of position-measuring device20is enabled only when the supply voltage has exceeded a specific voltage level in a stable manner. The reset signal may be supplied both to peripheral units of second subassembly20.2(in the illustrated example, to communications unit30and signal-processing unit31) and to first subassembly20.1, via electrical lines21.

Voltage-supply unit33stabilizes a supply voltage supplied to position-measuring device20by control unit50, e. g., via data-transmission cable52, and/or adapts the voltage level to the requirements of the components of the position-measuring device or first subassembly20.1and second subassembly20.2. This may require voltage-supply unit33to provide multiple different outputs, possibly featuring different voltages, and to transmit them via electrical lines21to first subassembly20.1. In the same manner, voltage-supply unit33may be suitable to generate one or more constant output voltage(s) from a variable input voltage.

In this exemplary embodiment, memory unit34is adapted to store the data held in initialization memory70. Memory unit34is able to be read out and programmed via internal interface38. The access to memory unit34by control unit50may take place via device interface36and internal interface38with the aid of communications unit30.

Position-measuring device20is operable in at least two operating modes, e.g., in a standard operating mode and in an initialization mode. The standard operating mode is the operating mode in which position-measuring device20is used as intended for measuring position values and for their transmission to a control unit50. The measuring and transmitting of the position values may be controlled by commands from control unit50. Since first subassembly20.1of position-measuring device20is to be suitable for an operation in radiation region A, all components of first subassembly20.1that are required for the operation in the standard operating mode are provided as radiation-hardened components, which means that they are suitable for use in a radiation region A of a machine.

However, because second subassembly20.2of position-measuring device20is arranged in the radiation-proof region B (to the right of the dashed line), it is unnecessary to provide the components of second subassembly20.2with radiation-resistant (radiation-hardened) components.

Initialization memory70, although arranged in first subassembly20.1, is not provided as a radiation-hardened memory and thus is actually unsuitable for use in radiation region A. For this reason, the initialization mode is provided to transmit the content of initialization memory70into a memory situated in the radiation-proof region B. In this exemplary embodiment, memory unit34is located in second subassembly20.2. Because the memory content of memory unit34rather than the content of initialization memory70is used in the standard operating mode, a change in the memory content of initialization memory70caused by the radiation with high-energy ionizing radiation has no effect on the performance reliability of position-measuring device20.

The use of a non-radiation-resistant (radiation-hardened) memory component in radiation region A of a machine or system has no harmful effect on the other components of first subassembly20.1, except for a possible change of the memory content. In other words, the performance reliability of first subassembly20.1in the standard operating mode is ensured, even if the memory component is exposed to high-energy ionizing radiation. Because the content of initialization memory70is relevant only in the initialization context, e.g., for the transmission into a memory operated in radiation-proof region B (in the exemplary embodiment, into memory unit34) and remains unused in the further operation, a change in the memory content of initialization memory70has no effect on the operativeness of position-measuring device20.

The activation of the initialization mode may be initiated automatically by control unit50, for example, directly following the switch-on of position-measuring device20. In the initialization mode, it is possible to transmit the data from initialization memory70to memory unit34. In this context, it is advantageous if the data in initialization memory70are protected by data-checking mechanisms, such as by a CRC code or by redundant encoding. In this manner, for example, it is possible to determine whether initialization memory70has already been modified. It may even be possible to implement the initialization despite damaged memory cells, by using error-correction algorithms. Following the copying of the data, position-measuring device20transitions to the standard operating mode, either automatically or once again initiated by control unit50.

Since it is generally sufficient to copy initialization memory70together with second subassembly20.2only once, that is, during the initialization of first subassembly20.1, a locking mechanism may be provided, which makes it possible to determine whether or not an initialization has already taken place. An identification memory71, for example, may be provided in first subassembly20.1for this purpose. This memory is adapted to be radiation-resistant and likewise equipped with an internal interface38.

In a first variant, identification memory71is programmable and is programmed appropriately once initialization memory70has been copied. A single memory cell may possibly suffice for this purpose. The programming advantageously is irreversible and may be accomplished by melt-through (fusing) of a circuit track provided for this purpose. Another possibility consists of implementing the memory cells as transistor structures and of providing a conductive connection between the emitter and base of the transistor structure (Zener zapping or Zener antifuse). By reading out identification memory71, it can be ascertained at any time whether the initialization has already taken place.

In another variant, an unequivocal identification (e.g., a serial number) that characterizes first subassembly20.1is stored in identification memory71. This unequivocal identification can also be stored in memory unit34of second subassembly20.2during the initialization. By comparing the identification in identification memory71with the identification stored in memory unit34, it is possible to ascertain whether or not an initialization has already occurred. In the former case, position-measuring device20may immediately be switched into the standard operating mode.

Based on the content of identification memory71, possibly in conjunction with the identification stored in memory unit34, control unit50is therefore able to decide whether an initialization will have to take place. As an additional safety measure, a safety query may be provided, for example, in that control unit50first displays the ascertained necessity of an initialization on a display unit (screen) and starts the initialization only after a service technician enables the initialization, e.g., the copying of the memory content of initialization memory70into memory unit34, using an input device (keyboard, mouse, etc.), by a positive answer to the security query. In this manner, the service technician is able to recheck the correct assignment between first subassembly20.1and second subassembly20.2prior to the initialization.

FIG. 3is a block diagram of a position-measuring device20according to an example embodiment of the present invention. Components that were already described in conjunction withFIG. 2have the same reference numeral and will not be described again.

In this exemplary embodiment, second subassembly20.2additionally includes a microcontroller72, which is used as initialization unit. Microcontroller72is equipped with an internal interface38, and thus is able to communicate with components of position-measuring device20that likewise have an internal interface38and are interconnected via this interface. The foregoing applies especially to initialization memory70and memory unit34.

The initialization, e.g., especially the copying of the data of initialization memory70into memory unit34, may be accomplished by microcontroller72. Internal interface38of microcontroller72is arranged as a master interface for this purpose.

An advantage of this system is that the initialization is able to be performed in an autonomous manner, e.g., without the involvement of control unit50. For example, after the switch-on, microcontroller72is able to determine on the basis of the content of identification memory71or by comparing the identification stored in initialization memory71with the identification stored in memory unit34(according to the two variants described above) whether an initialization is required. Accordingly, in the first case, it is able to switch position-measuring device20into the initialization mode, copy the content of initialization memory70into memory unit34, and then switch over to the standard operating mode.

As an alternative, the initialization in this exemplary embodiment is also able to be initiated by control unit50, but it is microcontroller72that implements the copying operation.

FIG. 4is a block diagram of a position-measuring device20according to an example embodiment of the present invention. Components that were already described in previous exemplary embodiments bear the same reference numerals.

In a deviation from the previously described exemplary embodiments, initialization memory70, memory unit34, and microcontroller72are connected via a separate memory interface48. In addition, an identification memory71may be provided here, as well, which likewise has a memory interface48. An interface that is already available in conventional memory units34may be used as memory interface48, such as an I2C interface, for example.

Microcontroller72may additionally be provided with an internal interface38. This creates a communication channel between control unit50(via device interface36and internal interface38) and microcontroller72.

Also in a deviation from the exemplary embodiments described with reference toFIGS. 2 and 3, instead of signal-processing unit31in second subassembly20.2, a signal-processing unit41is situated in first subassembly20.1. This has the advantage that a digital absolute position value P is already generated in first subassembly20.1, which may be transmitted via internal interface38to communications unit30of second subassembly20.2. Since the data transmission takes place within the framework of a data-transmission protocol, a secure transmission of the digital absolute position values P to second subassembly20.2is able to be ensured by suitable measures (e.g., the generation and transmission of check sums, etc.). This applies especially when the physical distance between first subassembly201and second subassembly20.2is large (several meters) due to the distance between radiation region A and radiation-proof region B.

In order to achieve the best possible interference security in the data transmission between signal-processing unit41and communications unit30, a differential data transmission, e.g., according to the RS-485 standard, is preferably used for the physical transmission in the case of internal interface38, as well. However, because the corresponding driver components have the previously mentioned drawbacks (high price, problematic availability, large size), the physical transmission of the data may also be undertaken with the aid of single-ended digital signals. In all cases, electrical lines21via which the data transmission is carried out must be adapted to the selected physical transmission.

In addition to internal interface38, signal-processing unit41also includes a memory interface48. This allows it to read out or write memory contents of memory unit34directly, without a detour by communications unit30. This, for example, reduces the loading of internal interface38, which is advantageous in particular during the standard operating mode, in which internal interface38is predominantly required for transmitting position data P.

All methods for the initialization that have already been described in connection with the previous exemplary embodiments are likewise able to be implemented using the architecture illustrated inFIG. 4.

FIG. 4illustrates yet another advantageous possibility for initiating the copying of data from initialization memory70to memory unit34, e.g., with the aid of a signal transducer73and a switching element74, which are provided on the housing of second subassembly20.2. If microcontroller72(or control unit50) detects, for example, based on the content of initialization memory72, that no initialization has taken place yet for first subassembly20.1, then the initialization mode and the copying procedure will not be started right away, but the service technician working on the system will first be informed with the aid of a signal from signal transducer73(e.g., lighting or blinking of a lamp) that an initialization needs to take place. The transition into the initialization mode is started only after the service technician operates switching element74(e.g., a push-button switch). In this manner, similar to the first exemplary embodiment, a security query is introduced in the initialization of a new first subassembly20.1, which enables the service technician to check once again whether new first subassembly20.1was indeed connected to the correct second subassembly20.2. Here, too, the transmission of the data from initialization memory70to memory unit34is started only once the security query has been answered positively (actuation of the switching element).

If device interface36and internal interface38have the same configuration, communications unit30may also include only the electromechanical connection (plug connector and electrical lines) between device interface36and internal interface38. There is also the option of not providing any communications unit30at all in second subassembly20.2.

The division selected inFIG. 4is especially advantageous because in modern position-measuring devices20, detector unit24and signal-processing unit41with corresponding interfaces38,48are often jointly integrated in a large-scale integration module60(ASIC or, in case of optical scanning, Opto-ASIC). This means that only the large-scale integration module60needs to be properly readied for use in a system in which position-measuring device20may be exposed to ionising, high-energy radiation, since the other components of the first subassembly, e.g., light source25and measuring standard22, already have the suitability for use in radiation region A, without requiring modifications.

As illustrated inFIG. 4, second subassembly20.2may be arranged in its own separate housing, physically separate from control unit50. This has the advantage that control unit50need not know at all that position-measuring device20consists of two subassemblies. In systems that already use absolute position-measuring devices which are protected from the occurring radiation by complex shielding measures (such as lead coating), it is therefore particularly easy to exchange these position-measuring devices for position-measuring devices20and to remove the undesired weight of the shield. All that is required is a simple check regarding the compatibility of device interface36.

It is also possible, as indicated by the block indicated as a dash-dotted line, to integrate second subassembly20.2into a control unit50′.

FIG. 5illustrates a position-measuring device20according to an example embodiment of the present invention. Here, again, components that were already described in the previous exemplary embodiments, bear the same reference numerals.

In a deviation from the previously described exemplary embodiments, no memory unit is provided in second subassembly20.2. Instead, a memory unit54suitable for storing the data of initialization memory70is provided in control unit50. Accordingly, during the initialization of position-measuring device20or in the exchange of first subassembly20.1, the content of initialization memory70, especially the data required in the standard operating mode, are copied from initialization memory70into memory unit54. The copying process is executed by control unit50, the access to the initialization memory takes place via device interface36and internal interface38, as previously described. In this exemplary embodiment, too, a security query may be provided prior to starting the copying process. During the standard operating mode, the data stored in memory unit54are then accessed.