WO2008131914A1

WO2008131914A1 - Synchronisation bus system, communication units for a synchronisation bus system, and method for exchanging messages for temporal synchronisation

Info

Publication number: WO2008131914A1
Application number: PCT/EP2008/003338
Authority: WO
Inventors: Anton Fuchs; Rudolf Kern; Frank Poxleitner; Otto Ruck
Original assignee: Carl Zeiss Industrielle Messtechnik Gmbh
Priority date: 2007-04-27
Filing date: 2008-04-21
Publication date: 2008-11-06
Also published as: DE102007020440B4; DE102007020440A1

Abstract

The invention relates to a synchronisation bus system (1) for enabling an exchange of messages (SN, aNj) between components. Said system comprises communication units (KE1-KEn) for the components for exchanging the messages (SN, aNj) by means of a transmission medium (3), the communication units (KE1-KEn) comprising a clock for providing a time signal for the respective components thereof. One of the communication units (KE1-KEn) comprises an emission unit for emitting messages (SN, aNj) via the transmission medium (3) and is operated as a transmitter unit which emits a synchronisation message (SN) in regular time intervals ΔT in such a way that it is synchronised with the time signal of the clock thereof. The remaining communication units (KE1-KEn) comprise a receiving unit for receiving messages (SN, aNj) and are operated as synchronised units which synchronise their clock with the clock of the transmitter unit for a successful reception of the synchronisation message (SN). The transmitter unit comprises a receiving unit and the synchronised units comprise an emission unit, and the communication units (KE1-KEn) are designed in such a way as to send and receive asynchronous messages (SN, aNj) via the transmission medium (3), asynchronously in relation to a clock pulse pre-defined by the transmitted synchronisation messages. The invention also relates to communication units and a method for the exchange of messages for temporal synchronisation.

Description

Synchronization bus system, communication units for a synchronization bus system and method for exchanging messages for time synchronization

The invention relates to a synchronization bus system, communication units and a method for exchanging messages between components, in particular components of a mechatronic system, for example a coordinate measuring machine, for time synchronization.

A large number of systems, for example mechatronic systems which comprise a plurality of components, depend on the individual components executing work or method steps synchronized in time. Such mechatronic systems include, for example, coordinate measuring machines which have one or more sensor carriers and one or more sensors which are arranged on the sensor carrier (s). Furthermore, a controller is provided, which is communicatively connected to the sensor carrier (s) and / or the sensor (s). All of these units are considered components of a coordinate measuring machine. In order to carry out a coordinate measurement, the individual sensor carriers and sensors must perform synchronized movements in time and / or detect measuring signals.

In the prior art, it is known to connect components of such mechatronic systems by means of a communication system. A known bus system is the CAN bus system (controller array network bus system), which is used for example frequently in the automotive industry. In the CAN bus system, different interconnected components can equally access a transmission medium. The individual transmitted messages are each assigned an identifier comprising several bits, which specifies a priority of the individual transmitted messages. In a simultaneous access of two components that message is transmitted, whose identifier has a higher priority. Over a CAN bus system can thus not synchronized by the individual components, ie asynchronously, to a possibly prevailing system time are exchanged. However, since a larger number of bits, ie information units, have to be exchanged at each transmission, a CAN bus is limited in its real-time capability in time-critical applications. Furthermore, synchronization to the time specified by a watch unit of one of the components is not provided in the protocol. Instead, the clock units of the individual communication units of the individual components are respectively resynchronized by means of a synchronization bit transmitted with the messages. In this case, a synchronization depends on which runtime differences the individual components have relative to one another. Since the synchronization is carried out by messages of different components, which usually have different runtime differences for a component, the synchronization fluctuates around these runtime differences.

In the prior art other systems are known in which a timer transmits a synchronization message to the other components of the system which synchronize their clock units according to the received synchronization message. The clock units of the individual components are thus synchronized. With regard to an "absolute time", the individual clocks of the components can each differ from one another by a transit time which the synchronization message from the timer to the respective component requires. However, because this run time is constant, the synchronization does not vary relative to the clock of the timer. If such a temporal synchronization is to be implemented permanently on a clock unit of a component in a CAN bus system, this requires complex logic in order to trigger a transmission of a specific message synchronized with a clock unit of the component. In this case, a multiplicity of bits, ie information units, would have to be transmitted, so that this is not suitable for time-critical applications. Furthermore, there is no synchronization to an edge change. Rather, a signal is sampled at intervals. A change from one interval to the next is used as a synchronization pulse. The sampling time, ie a sampling interval, remains as inaccuracy. In addition to having a precise synchronous clock signal in the components, it is often necessary for components to synchronize in time to events detected by another component. Transmission of such event information is not satisfactorily possible in time-critical applications using known bus systems.

The invention is therefore based on the technical object of providing a synchronization bus system, communication units for this purpose and a method for exchanging messages for time synchronization of components, on the one hand synchronization to a predetermined by a Uhreinheit time signal and in addition a transmission of asynchronous messages of the individual Enable components linked via the bus system.

The object is achieved by a synchronization bus system with the features of claim 1, a method having the features of claim 10 and a communication unit with the features of claim 19. Advantageous embodiments of the invention will become apparent from the dependent claims.

For such a synchronization bus system for facilitating an exchange of messages between components, it is provided that this synchronization bus system comprises communication units of the components for exchanging the messages via a transmission medium, the communication units comprising a clock for providing a time signal for their respective component and one of the communication units a transmitting unit for transmitting messages over the transmission medium and is operated as a transmitter unit which transmits a message called synchronization message via the transmission medium at regular time intervals synchronized with the time signal of their clock and the remaining communication units comprise a receiving unit for receiving messages and operated as synchronized units which, upon successful reception of the synchronization message, sets its clock with the clock of the Synchronize encoder unit, according to the invention, the transmitter unit comprises a receiving unit and the synchronized units comprise a transmitting unit and the communication units are adapted to send and receive asynchronous to a predetermined by the transmitted synchronization messages clock asynchronous messages on the transmission medium, wherein the transmission medium has a transmission state in which at least one of the messages is transmitted, or may take a free state in which none of the messages is transmitted, and wherein the communication units are configured to start transmitting a pending message for transmission only when the transmission medium is idle. As a transmission of a message synchronized with the time signal, a transmission is considered which accesses the transmission medium at a time determined on the basis of the time signal and the transmission of the message begins. Such a synchronization bus system offers the advantage that, on the one hand, the clock units of the individual components are synchronized rigidly with one another. However, it is also possible to inform the other components asynchronously about a occurred event. This makes it possible to temporally synchronize different components in their actions. If an event occurring at one of the components is to be used to initiate work or method steps on another component, a timely transmission of this event occurring by means of an asynchronous message with the aid of the bus system according to the invention is possible. As a result, complex procedures and workflows can be easily realized. Nevertheless, it is ensured that all components have clock signals that are synchronized to a single clock. This ensures that the individual work and process steps that perform the individual components can be performed synchronously in time. A communication unit according to the invention for such a synchronization bus system thus comprises a receiving unit for receiving messages transmitted via a transmission medium from other communication units, a transmitting unit for transmitting messages to the other communication units via the transmission medium, a clock unit for providing a time signal, wherein the communication unit is either synchronized Unit is operable, so that upon receipt of a message referred to as the synchronization message, the watch unit is synchronized, or operable as a transmitter unit which transmits a message called a synchronization message over the transmission medium at regular time intervals synchronized with the timing signal of its clock, logic being formed asynchronous to one transmitting the transmitted synchronization messages predetermined timing asynchronous messages over the transmission medium and receiving asynchronous messages, wherein the transmission medium may assume a transmission state in which at least one of the messages is transmitted or a free state in which none of the messages are transmitted, and wherein Sending a pending message for transmission is only started when the transmission medium is idle. Thus, with the synchronization bus system or the communication units for such a synchronization bus system, a method according to the invention for exchanging messages between components, in particular components of a mechatronic system, for example a coordinate measuring machine, for temporal synchronization is created in which one of the components of a communication unit designated as a transmitter unit a transmission medium synchronized with a time signal of a clock of the transmitter unit, a message called synchronization message is sent, and the communication units of the remaining components are operated as synchronized units, receive the synchronization messages and upon successful receipt of the synchronization message their respective clock Synchronize the clock of the encoder unit, wherein at least one of the communication units asynchronous to ei Send nem asynchronous messages via the transmission medium and the other communication units receive the asynchronous message nem specified by the transmitted synchronization messages clock. A largely collision-free transmission is achieved by starting a transmission only when the transmission medium is in the idle state. A time signal is understood to be a signal which enables a subdivision of the time into time intervals. In this case it is not necessary for an absolute time to be coded in the time signal. Rather, a signal indicating a time-regular clock can be used as a time signal be used. Accordingly, clocks and clock units in the sense of what is described here are also oscillators which generate an oscillating signal. In general, watches or Uhreinheiten comprise a quartz crystal, the high-frequency signal is reduced by a divider. The clock signal allows the components to divide the time between the synchronization messages.

In a preferred embodiment of the invention it is provided that the messages are each distinguished according to a content associated with them, wherein the content is encoded over a message transmission period. The message transmission duration is considered to be the time required for a communication unit to send the message, which is identical to the time it takes for another component to receive the message. To distinguish this is a runtime, which requires the message to be transmitted on the transmission medium from one component to the other. If, for example, a copper line is used as the transmission medium, the transit time for a message transmission is determined by a propagation speed of an electrical signal on the copper line. By contrast, the message transmission duration depends on the time span in which the transmitting unit transmits the message to the transmission medium. Coding the message content over a period of time, the message transmission duration, has the advantage of being easy to implement. An internal structure of the message, if it exists, need not be analyzed by the receiving unit.

In an advantageous embodiment of the invention priorities are assigned to the messages, the priority being proportional to the message transmission duration assigned to the message. High priority messages are thus encoded by a long message transmission time. This is to ensure that different messages that are reliably detected in the rare case that two components begin at the same time as sending a message, the higher priority message from all components. To be particularly advantageous, it has been found to provide that the messages are each assigned to each of the components and are each sent only by this component. This makes it possible to recognize based on the detected message and the sender of the message.

Preferably, the communication units are configured to each determine a time period in which the transmission medium is continuously in its transmission state and to identify the corresponding transmitted message based on this determined period of time.

In order to be able to intercept the rare case of a collision, which occurs when two components start simultaneously with the transmission of a message, it is provided in a preferred embodiment that the communication units check after transmission whether the transmission medium changes to a free state, and if this is not the case, then detect a collision and resend the message sent as soon as the transmission medium changes to the idle state. Excluded from this are synchronization messages, which are sent only synchronized in time with the clock signal of the encoder unit. The communication unit, which determines that the transmission medium does not go to the idle state after transmission, may also determine the amount of time that elapses before the transmission medium again changes to the idle state. This determined time span plus the amount of time that this communication unit used to send its own message, i. of the

Message transmission duration of the message sent by this communication unit results in the message transmission duration of the message sent by the other communication unit. The communication unit that detected the collision can thus uniquely identify the message that has collided with its own sent message. The remaining components or communication units of the synchronization bus system can not notice such a collision. Therefore, resending the shorter message having a lower priority is necessary. The occurring here time delay must be accepted. It is usually far below the times that must be waited in known bus systems for access to submit an asynchronous message.

In order to signal to the remaining units that a message was affected by a collision, it is provided in a preferred embodiment of the invention that the individual communication units are each assigned two, preferably priority-adjacent, messages. Preferably, the priority lower message is sent if no collision has occurred. The other, preferably priority adjacent, higher priority message is sent only in the case where a collision occurred while sending the lower priority message. As a result, a signaling of a collision is possible in a simple manner.

The synchronization bus system is usually designed such that the regular time intervals are dimensioned such that the individual clock units remain synchronized even if there is no synchronization message over a plurality of these time intervals. This means that the individual time signals of the clocks change only within a predetermined tolerance range relative to each other. Therefore, the individual communication units can detect an absence of a synchronization message if an asynchronous message is transmitted over the transmission medium in the corresponding time window for the synchronization message. In order to "destroy" any asynchronous message during synchronization, it is provided in a preferred embodiment of the invention that the synchronization message is assigned the shortest message transmission duration of the different messages.

In order to minimize a collision probability of messages, in a preferred embodiment it is provided that the shortest message transmission duration is longer than the maximum signal propagation time on the transmission medium between two of the communication units. The signal propagation time is considered to be the time that elapses between starting the transmission of a message to another of the components and the beginning of receiving the message by the other component. In order to ensure a reliable differentiation of the individual messages sent, even in the event of an occurring collision, it is provided in a preferred embodiment that the message transmission times of the various messages each differ by a time period which is greater than a maximum signal propagation time, preferably greater than a double of maximum signal transit time on which transmission medium is between two of the communication units. This ensures that in the event of a collision of two messages sent simultaneously to two communication units, their higher-priority message, ie the message with the longer message transmission duration, can be reliably identified at any point in the synchronization bus system. If the time difference of the message transmission duration of two different messages is twice the maximum signal propagation time, these messages, if they are sent at the communication units at the same time, between which the maximum signal propagation time occurs, of communication units that have no or a small "signal delay" of one of the two transmitting components can not be reliably distinguished.

The features of the method according to the invention or of the communication units according to the invention have the same advantages as the corresponding features of the synchronization bus system.

The invention will be explained in more detail below with reference to a preferred embodiment with reference to a drawing. Hereby show:

1 shows a schematic representation of a synchronization bus system with several components;

Fig. 2-6 an occurrence of messages to be transmitted, plotted against time and a corresponding state diagram of a transmission medium plotted against time; Fig. 7 is a schematic flow diagram of a method for communicating messages; and

Fig. 8 is a schematic view of a coordinate measuring system.

In Fig. 1, a synchronization bus system 1 is shown schematically. The synchronization bus system 1 comprises components designated as controllers S1, S2,..., Sn. The control units SI-Sn may be any desired mechatronic components, for example probes, rotary swivel joints, control devices, evaluation units, display devices, operating devices, etc. In the illustrated embodiment according to FIG. 1 of the synchronization bus system 1, the control units SI-Sn each comprise an integrated transmitting and receiving unit SEI-SEn. The illustrated transmitting and receiving units SEI-SEn are RS 485 transceivers. The transmitting and receiving units SEI-SEn are connected to one another via a transmission medium 3, which comprises two lines 5, preferably made of copper and preferably twisted. The transmitting and receiving units may be implemented separately in other embodiments. Also, the transmission medium can be configured differently. If an optical transmission is selected, the transmission medium can be, for example, an optical waveguide. Likewise, a fluid surrounding the components or even a vacuum may serve as a transmission medium. In such a case, a receiving unit may be a photosensitive electronic component, for example a phototransistor or a photosensitive resistor. The transmitting unit may comprise a light emitting diode or laser diode. The person skilled in various transmission and receiving units and corresponding transmission media are known. In the case of optical transmission, infrared, sound or radio transmission, the transmission medium does not necessarily have to be materialized separately. Rather, adapted to the transmitting and receiving units, a fluid or a vacuum can serve as a transmission medium. What is decisive is that the transmission medium can occupy at least two distinguishable states, wherein the one state, a transmission state, is assumed when a message is transmitted via the transmission medium. The other state, which is referred to as a free state is occupied by the transmission medium when no message is transmitted over the transmission medium. In particular, the transmission state may have other distinguishable substates, which are not of interest here, however. The term "occupying a state" is to be understood here in the sense that "one state can be assigned to the transmission medium" in each case.

The transmitting and receiving units SEI-SEn are components of communication units KEI-KEn. The control units SEI-SEn can themselves be designed as communication units. In addition to the transmitting and receiving units SEI-SEn, the communication units KEI-KEn each comprise a clock unit UEI-UEn, each of which provides a time signal for its control unit SEI-SEn. Furthermore, the communication units KEI-KEn each comprise a logic unit LEI-LEn. The logic units LEI-LEn control both the clock units UEI-UEn and the corresponding transmitting and receiving units SEI-SEn. They also process message transfer requests provided by control units StEI StEn of the respective controllers SEI-SEn for transmission. In addition, they prepare signals transmitted via the transmission medium 3 and make available received messages to the control units StEI-StEn.

The control units StEI-StEn and the logic units LEI-LEn can each also be integrated into a common integrated control unit. The logic units are preferably designed such that the individual communication units KEI-KEn can each be operated selectively either as a transmitter unit or as a synchronized unit. What is meant by this is explained in more detail below. A corresponding selection can be made, for example, via a switch (not shown) arranged in the logic unit. If the logic is executed programmatically, a selection can advantageously be made via a software-supported configuration.

In FIG. 2, synchronization messages SN are plotted on a time axis 11 in an upper part. Left edges 13 of the synchronization messages SN specify the so-called synchronization times tj and t _{i + 1} at which a synchronization of the clock units of a synchronization bus system should take place. (A definition would also be possible in which the right edges 14 are defined as synchronization times.) A time difference .DELTA.t = t.sub.i + 1-t.sub.i is a predetermined period of time, after which a component formed as a transmitter unit, ie, for example, control unit S1 according to FIG , in each case sends a synchronization message via the transmission medium. In a lower part of FIG. 2, a state of the transmission medium in the form of a state diagram 15 is plotted against time. When using an RS 485 interface as the transmitting and receiving unit, the state diagram corresponds to a voltage difference diagram of the lines 5 of the transmission medium 3 according to FIG. 1.

Before the synchronization time tj, the transmission medium is in the idle state. This means that no message is transmitted over the transmission medium. At the time tj, the transmission of the synchronization message SN begins. The transmission medium changes to the transmission state. The transmission medium remains in the transmission state for a transmission duration Δts _{N of} the synchronization message SN. At a time tj + .DELTA.t _SN the transmission medium changes back to the idle state. After a predetermined period ΔT = t _{i + 1} - tj has passed, the synchronization message SN is sent again via the transmission medium. Accordingly, the transmission medium again changes to the transmission state at time t _{i +} i for a transmission duration ΔtsN.

In addition to the synchronization messages sent by the transmitter unit, asynchronous messages may be sent from the transmitter unit or other communication units (controllers) via the transmission medium.

In Fig. 3 in the upper part again for transmission pending messages and in the lower part, the state diagram of the transmission medium are shown.

In addition to the synchronization messages SN asynchronous messages aN2 and aN3 are sent, for example, from a controller 2 and a controller 3. Left edges 13 indicate the respective times t _aN2 and t _aN3 to which a message transmission is requested accordingly. In order to differentiate visually the individual messages, the different messages SN, aN2, aN3 each have a different hatching. This is maintained by all figures. The synchronization messages SN have an obliquely hatching from top left to bottom right. The asynchronous message aN2 of the control unit 2 has a horizontal hatching and the asynchronous message aN3 of the control unit 3 has a vertical hatching. An extension along the time axis 11 indicates in each case a message transmission duration Δt _S N, Δt _a N2, Δt _a N ₃ assigned to the corresponding message. In the lower part of Fig. 3, the corresponding state diagram of the transmission medium is plotted against time. It will be appreciated that all messages, both the synchronization message SN and the asynchronous messages aN2 and aN3, can be transmitted without interference. Based on the length of time in which the transmission medium remains in the transmission state, each communication unit, which is connected to the transmission medium, identify the respective message.

FIG. 4 shows a case in which the asynchronous message aN2 of the control unit 2 is to be transmitted at a time t _aN2 'whose time from the synchronization time tj is less than the transmission time Δt _{aN2 of} the asynchronous message aN2 of the second control unit. This means that the transmission medium is in the transmission state when the control unit 1 wants to transmit a synchronization message SN. If the control unit 1 were to send this message to the transmission medium, the other communication units of the other control units would not be able to recognize this. However, since the other communication units all have a clock unit, they can independently recognize the time at which the synchronization message should be transmitted. Therefore, even in this case, the synchronization event is not lost. The clock units are designed such that the once synchronized time signals of the various clock units remain synchronous for a plurality of predetermined time periods ΔT (synchronization cycles), even if no synchronization message SN (synchronization pulse) has been received from the synchronized communication units. The synchronization bus system can thus handle well individual asynchronous messages, such as the asynchronous message aN2 of the control unit 2 in the example of FIG. 4, which are transmitted during a synchronization time tj, t _{i + 1} .

FIG. 5 shows a case in which a request for the transmission of an asynchronous message aN3 of the control device 3 takes place at a time t _3N3 'at which a message transmission of an asynchronous message aN2 of the control device 2 still lasts. In this case, the communication unit of the controller 3 notices that the transmission medium is not in the idle state. It waits for the reception of the asynchronous message, ie the asynchronous message aN2 of the control unit 2, and then transmits, after the transmission medium has returned to the idle state, its asynchronous message aN3. The small time lag between the time

to which the message transmission is requested, and the time t _aN3 ^R , to which the transmission actually begins, is usually so minimal that it does not further affect the functioning of the overall system. If, for example, a coordinate measuring machine is realized by means of the components (control devices) of the synchronization bus system 1 according to FIG. 1, the predetermined time interval .DELTA.T is 1 ms (corresponds to 1 kHz) and message transmission duration of the synchronization messages 3 .mu.s, the asynchronous message aN2 of the control _device 2 .DELTA.t _aN2 = 5 _.mu.s and the message transmission time .DELTA.t _aN 3 of the asynchronous message aN3 of the control unit 3 .DELTA.t _aN3 = 7 _microseconds , so is an offset here a maximum message transmission duration of the first message sent. If the components, which are designed, for example, as movable actuators, execute movements at a speed in the range of a few mm / s, synchronization inaccuracies in the range of a few microseconds (μs) cause location inaccuracies of the actuating elements in the range of micrometers (μm) or less.

In Fig. 6, finally, the rarely occurring case is shown, in which two

Control units at the same time (t _aN 2 = t ₃ N3) try to transmit a message. By doing In the case illustrated, the control unit 2 and the control unit 3 each attempt to transmit the asynchronous messages aN2 and aN3 corresponding to them. Both begin the transmission at the same time. The transmission medium remains in the transmission state as long as one of the two messages is sent. This means that the message aN3 with the longer message transmission duration determines the retention of the transmission medium in the transmission state. Thus, of the communication units connected to the transmission medium, it is merely detected that the message aN3 has been transmitted with the longer message transmission duration. A message with a longer message transmission duration thus has a higher priority than a message which has a shorter message transmission duration.

The controller 2 may determine the collision that it checks after the end of the transmission of its asynchronous message aN2, whether the transmission medium changes to the idle state. If this is not the case, then a collision can be detected. If the control unit 2 now determines the period of time Δtciz in which the transmission medium remains in the transmission state after the transmission of its own asynchronous message aN2 has ended, this time interval Δtoz can be used to determine the message transmission duration of the collision message. For this purpose, the determined time interval Δtüz is added to the message transmission _duration Δt _{aN2 of} the message itself sent. About the message transmission duration .DELTA.t _a N3 = .DELTA.tüz ⁺ .DELTA.t _a N2 thus obtained a unique identification of the transmitted message is possible. This requires that the individual messages each have an individual message transmission duration. Particularly advantageous is provided that each message is assigned to exactly one control unit. This means that several ECUs can be assigned to one ECU. In particular, the control unit 1 used as the transmitter unit can also send asynchronous messages in addition to the synchronization messages.

After the asynchronous message aN3 has finished transmitting and the transmission medium has returned to the idle state, the time is up taN2 ^R the asynchronous message aN2 slightly delayed with respect to the request time t _aN2 sent.

In applications in which it is necessary to make a collision recognizable also for the receivers, it can be provided that two different messages are provided for each transmitted information. One of the messages is sent if, at the time of the message transfer request, the transmission medium is idle and a message transfer is started immediately. The other of the messages is sent when the message transmission medium is not idle at the time the request for transmission of the message is made, or at the end of the message transmission that a message has been found to have collided with a message of higher priority from another communication unit.

Referring to Figure 7, a schematic flow diagram of a method for communicating messages for time synchronization purposes 100 is shown. Illustrated by way of example are both the method steps which are carried out in a transmitter unit as well as in a synchronized unit. At the appropriate point, it is pointed out which method steps are executed only in one or the other unit. At the same time and continuously, on the one hand, the transmission medium is monitored 103, a transmission request is monitored 105 and a time signal 107 is generated by a clock unit. The generated time signal can be provided to other components, for example a control device, of its own component. In the encoder unit is additionally checked whether the regular predetermined time .DELTA.T has passed, after which a new synchronization message is to be sent 109. If this is not the case, the generation of the time signal is continued. However, if the period of time Δ T has elapsed, then a synchronization message 111 is defined as a message to be sent. In the preferred embodiment, which is also based on the method shown here, the asynchronous messages have a higher priority than the synchronization message. Therefore, it is queried whether there is an asynchronous message to be sent 113. If this is the case, then the Synchronization message are not transmitted and the generation of the time signal is continued until the next time the period of time .DELTA.T has passed.

However, if the query 113 has shown that there is no asynchronous message to be sent, it is next checked whether the transmission medium is in the transmission state 115. If this is not the case, then the right no branch 117 is followed. The procedures associated with sending a message are connected by dashed lines in FIG. Since the transmission medium is not in the transmission state, it must be in the idle state. Now the message to be sent is sent to the transmission medium 119.

After the transmission of the message has ended, it is checked whether the transmission medium has changed to the idle state 121. If this is the case, then the transmitted message has been transmitted successfully. On the other hand, if the transmission medium has not changed to the idle state, then a collision is detected 123. The time span Δtciz in which the transmission medium remains in the transmission state 125 is then determined.

By adding the thus determined period of time Δttiz to the message transmission time At ₃ Nj of the message sent, the message transmission _duration At _{3Nk of} the collision message aNk is determined 127, which can subsequently be identified 129.

If a collision has previously occurred, the identified message can not be a synchronization message if the synchronization message has the lowest priority. As a result, the issuing of the identified received message is continued 131.

In order to check whether the collision occurred when sending an asynchronous message, it must be checked at least in the encoder unit whether there is an asynchronous message to be sent 133. If this is not the case, for example because the collision occurred when sending a synchronization message, the generation of the time signal 107 and the monitoring of the send request 105 and the monitoring of the transmission medium 103 are continued. If, on the other hand, an asynchronous message to be sent is present, method step 115 is continued, in which it is checked whether the transmission medium is in the transmission state. The further procedure is similar to the procedure described so far from step 115, unless the transmission medium is in the transmission state.

The monitoring of the transmission medium 103 is followed by the query as to whether the transmission medium is in the transmission state 115. If the transmission medium is in the transmission state, the time span in which the transmission medium remains in the transmission state is determined according to process block 125. Subsequently, the received message can be identified on the basis of the determined message transmission duration 129. A query 135 checks whether the identified message is a synchronization message 135 in a synchronized unit. If this is the case, the clock (for example an oscillator) becomes the own clock unit synchronized 137. Subsequently, the monitoring of the transmission medium 103 is continued. If, on the other hand, the identified message is not a synchronization message, the identified received message is output 131 and then the monitoring of the transmission medium 103 and the other simultaneously ongoing process actions, monitoring of the send request 105 and the generation of the time signal 107, are continued.

In the inquiry 139, whether there is a send request, it is detected whether such a send request for an asynchronous message aNj exists. If this is the case, then the asynchronous message aNj is set as the message to be sent 141. The further procedure is similar to the sending of a synchronization message from method step 115.

It will be understood by those skilled in the art that the examples described above are merely exemplary in nature. In particular, a precise design the communication units be executed differently. In this case, both the logic unit and the control unit can be implemented both by hardware and software. Preferably, the communication units are designed such that they can be operated both as a transmitter unit and as a synchronized unit. However, embodiments of synchronization bus systems are also conceivable in which communication units are used which can only be operated either as a transmitter unit or as a synchronized unit, as well as synchronization bus systems in which additionally units are used which can be operated either as transmitter units or as synchronized units are.

In the described embodiments, the synchronization message has been assigned the lowest priority. Other embodiments are conceivable in which the synchronization message is assigned an average or even the highest priority.

In order to enable unambiguous identification of the messages, the shortest message transmission time should be greater than a maximum signal propagation time between two communication units over the transmission medium. Further, the message transmission times of different messages should be different from each other by more than twice the maximum signal propagation time.

FIG. 8 schematically shows an exemplary coordinate measuring machine 50. The coordinate measuring machine 50 comprises a control unit 52 and mechanically coupled to each other an x-actuator 54, a y-actuator 56 and a z-actuator 58. The control unit 52 and the actuators 54-58 are components of the coordinate measuring machine 50. With the z-actuator is a probe 60 is connected, which can be positioned three-dimensionally in space about the actuators 54-58 to scan an object 62 in terms of its dimensions. Each actuator may effect a displacement of the probe along a direction of a coordinate system 61. In order to detect a contact of the probe 60 with the object 62, the z-actuator comprises a measuring sensor (not shown).

The control unit 52 is connected to the actuators 54-58 via a first bus 64, on which, for example, messages are exchanged by means of the CAN protocol, and a synchronization bus 66.

While instructions, measurement data, status information, etc., are exchanged via the first bus 64, the synchronization bus 66 serves to synchronize clocks of the controller 52 and the actuators 54-58. Furthermore, motion sequences are triggered via asynchronous messages and events, for example a start of movement, a reaching of a predetermined position, a detection of a measured value, etc., are signaled promptly to their occurrence. Here are individual events associated with individual messages that differ by their message transmission duration. Preferably, a message is sent only from one of the components (controller 52 or one of the actuators 54-58).

The asynchronous messages enable a synchronized execution of movements of the actuators 54-58 and a synchronized acquisition of status information and measurement data.

LIST OF REFERENCE NUMBERS

1 synchronization bus system

S1. S2, ..., Sn control units

SE1, SE2 ..., SEn transmitting and receiving units

3 transmission medium

5 lines

KE 1. KE2, ..., KEn communication units

UE1. UE2 UEn Uhreinheiten

StE1, StE2 StEn control units

SN synchronization message

11 timeline

13 left edge

14 right edge ti, t _{i +} i synchronization times

15 State diagram taNj Request time for transfer of an asynchronous message j

+ R IaNj Send time for an asynchronous transfer

Message j, which must be sent with a time delay

ΔtaNj message transmission time of the asynchronous

Message j aNj asynchronous message j

50 coordinate measuring machine

52 control unit

54 x actuator

56 y actuator

58 z actuator

60 probe

61 coordinate system

62 object

64 first bus (CAN bus)

66 synchronization bus 100 Procedure for exchanging messages for a time synchronization

103 Monitoring a transmission medium

105 Monitoring a Send Request

107 generating a time signal

109 Query: Has a period of time elapsed?

111 Define the synchronization message as a message to be sent

113 Query: Is there an asynchronous message to send?

115 Query: Is the transmission medium in the transmission state?

117 right no branch

119 send message to send

121 Query: Has the transmission medium changed to idle status?

123 Detecting a collision

125 determining a time period in which the transmission medium remains in the transmission state 127 adding the determined time period to the

Message transmission duration of the sent message 129 Identification of the received message

131 Output the identified received message

133 Query: Is there an asynchronous message to send?

135 Query: Is the identified message a

Synchronization message?

137 Synchronizing the clock unit

139 Query: Is there a send request?

141 Asynchronous message is set as message to be sent

Claims

claims

A synchronization bus system (1) for enabling replacement of

Messages (SN, aNj) between components comprising communication units (KEI-KEn) of the components for exchanging the messages (SN, aNj) via a transmission medium (3), the communication units (KEI-KEn) having a clock for providing a time signal for their respective ones Component and one of the communication units (KEI-KEn) comprises a transmitting unit for transmitting messages (SN, aNj) via the transmission medium (3) and is operated as a transmitter unit, which synchronized at regular time intervals synchronized with the time signal of their clock as a synchronization message (SN ) and the remaining communication units (KEI-KEn) comprise a receiving unit for receiving messages (SN, aNj) and are operated as synchronized units which, upon successful reception of the synchronization message (SN), clock their clock Synchronize the encoder unit, characterized in that d the transmitter unit comprises a receiver unit and the synchronized units comprise a transmitter unit and the communication units (KEI-KEn) are designed to transmit and receive asynchronous messages (SN, aNj) via the transmission medium (3) asynchronously to a clock rate specified by the transmitted synchronization messages; wherein the transmission medium (3) can assume a transmission state in which at least one of the messages (SN, aNj) is transmitted, or a free state in which none of the messages (SN, aNj) is transmitted, and wherein the communication units (KEI-KEn ) are configured to start transmitting a pending message (SN, aNj) only when the transmission medium (3) is idle.

2. synchronization bus system (1) according to claim 1, characterized in that the communication units (KEI-KEn) after a transmission check whether the transmission medium (3) changes to the idle state, and if this is not the case, then detect a collision and send the transmitted message (aNj) again as soon as the transmission medium (3) has switched to the idle state.

3. synchronization bus system (1) according to claim 1 or 2, characterized in that the messages (SN, aNj) are each distinguished according to a content associated with them, wherein the content over a message transmission time (.DELTA.t _S N, .DELTA.t _a N2, .DELTA.t _a N ₃ ) is coded.

4. synchronization bus system (1) according to any one of the preceding claims, characterized in that the messages (SN, aNj) priorities are assigned, wherein a priority proportional to the message (SN, aNj) associated message transmission time (.DELTA.t _S N, .DELTA.t _a N2 , Δt _a N3).

5. synchronization bus system (1) according to one of the preceding claims, characterized in that the messages (SN, aNj) are each assigned to each of the components and are each sent only from this component.

6. synchronization bus system (1) according to any one of the preceding claims, characterized in that the communication units (KEI-KEn) are adapted to each determine a period of time in which the transmission medium (3) is continuously in its transmission state, and the corresponding transmitted message (SN, aNj) (highest priority) based on this time period.

7. Synchronization bus system (1) according to one of the preceding claims, characterized in that the synchronization message (SN) is associated with the shortest message transmission duration (Δt _S N, Δt _a N2, Δt ₃ N3) of the different messages (SN, aNj).

8. synchronization bus system (1) according to any one of the preceding claims, characterized in that the shortest message transmission time (.DELTA.t _S N, .DELTAtaN2, .DELTAtaN3) is longer than the maximum signal propagation time on the transmission medium (3) between two of the communication units (KEI-KEn).

9. Synchronization bus system (1) according to any one of the preceding claims, characterized in that the message transmission times (Δts _N , ΔtaN2, ΔtaNß) of the various messages (SN, aNj) each differ by a time greater than a maximum signal propagation time on the transmission medium (3) is between two of the communication units (KEI-KEn).

10. A method for exchanging messages (SN, aNj) between components, in particular components of a mechatronic system, for temporal synchronization, in which of a designated as a transmitter unit communication unit (KEI-KEn) one of the components via a transmission medium (3) in temporally regular Intervals synchronized with a time signal of a clock of the encoder unit as a synchronization message (SN) called the messages (SN, aNj) is sent, and communication units (KEI-KEn) of the remaining of the components are operated as synchronized units receiving the synchronization message (SN) and upon successful receipt of the synchronization message (SN), synchronize its respective clock with the clock of the transmitter unit, characterized in that at least one of the communication units (KEI-KEn) asynchronous to a predetermined by the transmitted Synchronisationsnachtrichten clock asynchronous messages (SN, aNj) ü via the transmission medium (3) and the other communication units (KEI-KEn) receive the asynchronous message (aNj), wherein the transmission medium (3) a

Transmission state in which at least one of the messages (SN, aNj) is transmitted, or can assume a free state in which none of the messages (SN, aNj) is transmitted, and a transmission of a pending message (SN, aNj) is only started when the transmission medium (3) is in the idle state.

11. The method according to claim 10, characterized in that the communication units (KEI-KEn) after a transmission check whether the transmission medium (3) changes to the idle state, and if this is not the case, then detect a collision and the message sent (SN, aNj) again as soon as the transmission medium (3) has switched to the idle state.

12. The method according to claim 10 or 11, characterized in that the messages (SN, aNj) are each distinguished according to a content associated with them, wherein the content over a message transmission time (.DELTA.t _S N, .DELTA.t _a N2, .DELTA.t _a N3) is encoded ,

13. The method according to any one of claims 10 to 12, characterized in that the messages (SN, aNj) priorities are assigned, wherein a priority proportional to the message (SN, aNj) associated message transmission duration (ΔtsN .DELTA.t _a N2, .DELTA.t _a N3).

14. The method according to any one of claims 10 to 13, characterized in that the messages (SN, aNj) are each assigned to each of the components and are sent only by each of these components.

15. The method according to any one of claims 10 to 14, characterized in that the communication units (KEI-KEn) each determine a period of time in which the transmission medium (3) is continuously in its transmission state, and identifies the corresponding transmitted message based on this determined period of time becomes.

16. The method according to any one of claims 10 to 15, characterized in that the synchronization message (SN) is associated with the shortest message transmission duration (Δt _S N, Δt _a N2, Δt _a N3) of the different messages (SN, aNj).

17. The method according to any one of claims 10 to 16, characterized in that the shortest message transmission duration (ΔtsN, Δt _a N2, Δt _a N3) is longer than the maximum signal propagation time on the transmission medium (3) between two of the communication units (KEI-KEn) ,

18. The method according to any one of claims 10 to 17, characterized in that the message transmission periods (.DELTA.tsN, .DELTA.t _a N2, .DELTA.t _a N3) of the various messages (SN, aNj) each differ by a time period which is greater than a maximum signal propagation time the transmission medium (3) between two of the communication units (KEI-KEn) is.

19. Communication unit (KE1-KEn) for a synchronization bus system (1) according to one of claims 1 to 9, comprising a receiving unit for receiving messages (SN, aNj) sent via a transmission medium (3) from other communication units (KEI-KEn) Sending unit for sending messages (SN, aNj) to the other communication units (KEI-KEn) via the transmission medium (3), a clock unit for providing a time signal, wherein the communication unit (KEI-KEn) is operable as a synchronized unit, so that at receiving a synchronization message (SN) called the message (SN, aNj) the clock unit is synchronized, characterized in that a logic is formed asynchronous to a predetermined by the transmitted synchronization messages (SN) clock asynchronous messages (SN, aNj) on the Transmit transmission medium (3) and receive asynchronous messages (SN, aNj), wherein the transmission medium m (3) one

20. Communication unit (KEI-KEn) according to claim 19, characterized in that the logic unit is designed to check after sending a message (SN, aNj), whether the transmission medium (3) changes to the idle state and if this is not the case is to detect a collision therefrom and to send the transmitted message (SN, aNj) again as soon as the transmission medium (3) has switched to the idle state, provided that the transmitted message (SN, aNj) is not the synchronization message (SN).

21 communication unit (KEI-KEn) according to claim 19 or 20, characterized in that the logic is configured to distinguish the messages (SN ₁ aNj) each according to a content associated with them, wherein the content over a message transmission period (ΔtsN, Δt _a N2, Δt ₃ N3).

22. Communication unit (KEI-KEn) according to claim 19 or 21, characterized in that the communication unit (KEI-KEn) one of the messages (SN, aNj) with a predetermined

Message transmission duration (.DELTA.tsN, .DELTA.t _a N2, .DELTA.t _a N3) is assigned, which are transmitted from the other message transmission periods (.DELTA.t _S N, .DELTA.t _a N2, .DELTA.t _a N3) of the communication medium (3) from other communication units (KE1 KEn) Messages (SN, aNj) differs.

23 communication unit (KEI-KEn) according to claim 19 or 22, characterized in that the logic unit is adapted to each determine a period of time in which the transmission medium (3) is continuously in its transmission state, and the corresponding received message (SN, aNj) on the basis of this determined period of time.

24. Communication unit (KEI-KEn) according to claim 19 or 23, characterized in that the synchronization message (SN) is assigned the shortest message transmission duration (ΔtsN, Δt _a N2, Δt ₃ N3) of the different messages (SN, aNj).

25. Communication unit (KEI-KEn) according to claim 19 or 24, characterized in that the shortest message transmission duration (.DELTA.t _SN , .DELTA.tgN2, .DELTAtaN3) longer than the maximum signal propagation time on the transmission medium (3) to or from another communication unit (KEI KEn ).

26. Communication unit (KEI-KEn) according to claim 19 or 25, characterized in that the predetermined message transmission duration (.DELTA.t _SN , .DELTA.taN2, .DELTA.tgN3) of the message transmission times (.DELTA.ts N, .DELTA.t _a N2, .DELTA.t ₃ N3) of the remaining messages (SN, aNj) is each differentiated by a period greater than a maximum signal propagation time on the transmission medium (3) to or from another communication unit (KEI-KEn).

27. Communication unit (KEI-KEn) according to claim 19 or 26, characterized in that the communication unit (KEI-KEn) is operable as a transmitter unit, synchronized at regular time intervals synchronized with the time signal of their clock as a synchronization message (SN) message on the Transmission medium (3) sends.