Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-02-17
2001-02-06
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S503000, C375S356000
Reexamination Certificate
active
06185217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a timer synchronizing device and an initializing method for use in a communication system. In particular, the timer synchronizing device of the present invention can synchronize accurately timers of slave stations connected to a ring communication path.
2. Description of the Prior Art
Conventionally, respective timers connected to a ring communication path are synchronized using a specific communication frame. In the following, one such example will be described. In this example, timers on a ring communication path are synchronized according to SERCOS regulations.
FIG. 6
shows the structure of a conventional ring communication path which includes a master station
64
and slave stations
61
,
62
,
63
. The master station
64
outputs a specific communication frame called SYNC-TELEGRAM for timer synchronization. The frame is first received by the slave station
61
, which then corrects its own timer
66
according to the received frame. The slave station
61
also relays the received frame to its subsequent station, so that the slave station
62
receives the relayed frame and corrects its own timer
67
accordingly.
In this manner, respective slave stations connected to the ring communication path
65
sequentially receive the specific frame and correct their timers. This entire process for timer synchronization is completed when a timer correcting operation by the last connected slave station
63
is completed. It should be noted that the timing at which respective slave stations receive the specific frame is gradually delayed as the frame reaches the latter connected stations on the path as a result of a frame relaying process at each station. Because the delay is minimized by setting a 0.5 to 1.5 clock transmission delay at each slave station, disagreement among respective timers can be left uncorrected.
Another example will next be described with reference to FIG.
5
. In this example, timer synchronization is achieved with improved transfer efficiency by using a method including a communication frame exchanging process. “Exchanging a communication frame” refers to exchanging a part or the whole of a communication frame transferred through a ring communication path
5
, with transmission data
55
at its destination slave station.
In the following, a procedure in which slave stations receive a communication frame will be described.
A destination detection circuit
53
receives a communication frame, beginning with its leading bits. The circuit
53
then compares the destination address of the frame with the address of its own station, which is recorded in its own address storage
54
when the circuit
53
reads the destination address, so as to detect whether or not the received frame addresses its own station as a destination station. If the frame does address that station, the communication frame is supplied to a communication frame exchanging circuit
52
. If it does not, the frame is supplied to a relay circuit
51
. Every communication frame, including a frame for timer synchronization, is subjected to this destination detection process at each slave station, regardless of its destination. That is, frame transmission is always delayed due to this process (hereinafter this delay time being referred to as a relay process time). A relay process time caused at each station will accumulate as a frame passes through the respective slave stations performing relay processing on the path.
The accumulated relay process time results in a problem in a system, such as a machine tool, whose motors are controlled using this method. That is, reference times at respective motors may disagree with one another due to a relay process time, which is on the order of a few &mgr;s for each station, and this may further result in such a system forming an inaccurate trail. For instance, assuming that a relay process time is 6 &mgr;s and a feeding time of each motor is 20 m/min, the entire influence of the delay over the system sums up to be 2 &mgr;m.
As described above, the conventional timer synchronizing method cannot achieve accurate timer synchronization because of the presence of a transmission time delay, and thus cannot achieve accurate time synchronization among respective slave stations on a ring communication path. Therefore, if a master station and slave stations are connected such that a communication frame is transmitted among the stations at a subtle timing based on the timers which have been synchronized using the conventional method, transmission contents come to be faulty between the master and the slave stations. Moreover, the greater the number of slave stations connected to a path, the greater will be the time delay in latter connected slave stations along the path. Conclusively, the conventional timer synchronizing method in which a transmission time delay is left uncorrected is inappropriate to be used in a ring communication path which requires severe time accuracy.
SUMMARY OF THE INVENTION
The present invention has been conceived to overcome the above problems and aims to provide a timer synchronizing device and an initializing method for a communication system. A timer synchronizing device and an initializing method of this invention are used particularly in a system which employs a method including a communication frame exchanging process and thus causes a larger frame transmission delay than by other systems, such as a SERCOS system, which do not use such a process.
With this timer synchronizing device, respective timers of master and slave stations connected to a ring communication path can be synchronized without being affected by a communication time delay.
According to the present invention, there can be provided a timer synchronizing device for synchronizing timers of respective slave stations connected to a ring communication path by using a specific communication frame, comprising recognizer installed in a master station for recognizing the number of slave stations connected to the ring communication path, and their respective connection sequences; notifier installed in the master station for notifying the slave stations of transmission delay times according to the respective connection sequences; and correcter installed in the slave stations for correcting a time difference for synchronization between the timer of the master station and the timers of the slave stations.
Also, according to the present invention, there can be provided an initializing method for initializing communication addresses of slave stations connected to a ring communication path for synchronization of timers of the slave stations by using a specific communication frame, comprising a step in which a master station recognizes the number of the slave stations connected to the ring communication path and connection sequences thereof; a step in which the master station notifies the slave stations of transmission delay times according to the connection sequences; and a step in which the slave stations correct a time difference caused in synchronization between the timer of the master station and the timers of the slave stations.
Further, the above method further comprises a step in which the master station calculates the transmission delay times to notify the slave stations, based on an accumulated value of respective transmission delay times, of which the slave stations individually inform the master station at initialization.
According to the timer synchronizing device and an initializing method of the present invention, the timers of the master and slave stations connected to a ring communication path can be accurately synchronized when the slave stations receive a specific communication frame for timer synchronization. This is achievable even when the frame transmission between the master and slave stations includes a communication frame exchanging process, because a transmission delay time is defined individually for every slave station so that each slave station can correct its own timer by an ext
Ando Toru
Eba Koji
Kizou Hassan
Okuma Corporation
Oliff & Berridg,e PLC
Tsegaye Saba
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