Communication system, base communication device, and remote communication device

Abstract

A communication system according to the present disclosure comprises a plurality of communication devices. A first communication processing unit of a first communication device includes, in a communication packet, correction-related data pertaining to correction of a synchronization signal and transmits the communication packet to a second communication device. A first timing correction unit of the first communication device executes first timing correction processing corresponding to the correction-related data included in one communication packet after transmission of the one communication packet from the first communication device to the second communication device is started and before transmission of another communication packet to be transmitted following the transmission of the one communication packet from the first communication device to the second communication device is started.

Description

COMMUNICATION SYSTEM, BASE COMMUNICATION DEVICE AND REMOTE COMMUNICATION DEVICE - Patent application

[0001] The present disclosure relates to a communication system, a base communication device and a remote communication device.

[0002] Japanese Patent Publication No. 2012-508474 discloses a system in which a base communication device (master) and a remote communication device (slave) communicate in synchronization with each other.

[0003] There is a need for better communication systems, base communication devices and remote communication devices.

[0004] A first aspect of the present disclosure is a communication system including a plurality of communication devices, wherein a first communication device among the plurality of communication devices includes a first communication processing unit that executes communication processing, and a first timing correction unit that executes a first timing correction process that corrects the timing of a first synchronization signal that is a synchronization signal used when the first communication processing unit executes the communication processing, and a second communication device among the plurality of communication devices includes a second communication processing unit that executes the communication processing, and a second timing correction unit that executes a first timing correction process that corrects the timing of a second synchronization signal that is a synchronization signal used when the second communication processing unit executes the communication processing. and a second timing correction unit that performs timing correction processing No. 2, wherein the first communication processing unit includes correction-related data regarding correction of a synchronization signal in a communication packet and transmits the communication packet to the second communication device, and the first timing correction unit performs the first timing correction processing according to the correction-related data included in one communication packet after transmission of the one communication packet from the first communication device to the second communication device has started and before transmission of another communication packet to be transmitted after the one communication packet has started from the first communication device to the second communication device.

[0005] A second aspect of the present disclosure is a base communication device that communicates with a remote communication device, comprising: a communication processing unit that performs communication processing; and a timing correction unit that performs timing correction processing that corrects the timing of a synchronization signal used when the communication processing is performed by the communication processing unit, wherein the communication processing unit includes correction-related data related to the correction of the synchronization signal in a communication packet and transmits the packet to the remote communication device, and the timing correction unit performs the timing correction processing according to the correction-related data included in one communication packet after transmission of the one communication packet to the remote communication device has begun and before transmission of another communication packet to the remote communication device has begun after the one communication packet.

[0006] A third aspect of the present disclosure is a remote communication device that communicates with a base communication device, comprising: a communication processing unit that performs communication processing; and a timing correction unit that performs timing correction processing that corrects the timing of a synchronization signal used when the communication processing is performed by the communication processing unit, wherein a communication packet received by the communication processing unit from the base communication device includes correction-related data related to the correction of the synchronization signal, and the timing correction unit performs the timing correction processing according to the correction-related data included in one communication packet before another communication packet to be transmitted after the one communication packet is received by the communication processing unit.

[0007] FIG. 1 is a configuration diagram of a communication system according to one embodiment. FIG. 2 is a block diagram of a base communication device among the plurality of communication devices. FIG. 3A is a timing chart illustrating a simplified example of the timing of a synchronization signal. FIG. 3B is a timing chart illustrating a simplified example of the timing of a synchronization signal after correction when the synchronization signal is corrected. FIG. 4 is a block diagram of a remote communication device among the plurality of communication devices. FIG. 5 is a table illustrating the relationship between the deviation correction amount determined by the comparison result (comparison result) by the comparator, the tracking correction amount determined by the correction-related data, and the combined correction amount obtained by combining the deviation correction amount and the tracking correction amount. FIGS. 6A to 6D are each a schematic side-by-side diagram of a synchronization signal (first synchronization signal) in a first communication device and a timing chart of a synchronization signal (second synchronization signal) in a second communication device. FIG. 7 is a configuration diagram of a communication system according to a comparative example. FIG. 8 is a side-by-side diagram of a synchronization signal in a base communication device according to a comparative example and a timing chart of synchronization signals in a plurality of remote communication devices.

[0008] The base communication device performs communication processing based on a synchronization signal generated by the base communication device. On the other hand, the remote communication device performs communication processing based on a synchronization signal generated by the remote communication device. By synchronizing the synchronization signal of the base communication device and the synchronization signal of the remote communication device within a predetermined synchronization accuracy range, good communication can be achieved.

[0009] However, there is a problem that the timing of the synchronization signal of the base communication device and the timing of the synchronization signal of the remote communication device gradually become misaligned due to, for example, clock deviation between the base communication device and the remote communication device. Also, the synchronization signal of the base communication device may be corrected based on an external command. This correction may cause a problem that the timing of the synchronization signal of the base communication device and the timing of the synchronization signal of the remote communication device become misaligned.

[0010] Based on the above preliminary explanation, one embodiment will be described below.

[0011] In the following description, computer programs (computer software) are also referred to as computer program products. Computer program products are not limited to computer programs recorded on a recording medium, but also include computer programs transmitted, distributed, or downloaded via an information and communication network such as the Internet.

[0012] FIG. 1 is a diagram illustrating the configuration of a communication system 10 according to an embodiment.

[0013] The communication system 10 includes a plurality of communication devices 12. The plurality of communication devices 12 includes a base communication device 14 and a remote communication device 16. The plurality of communication devices 12 may include one or more remote communication devices 16. As shown in FIG. 1, the plurality of communication devices 12 may include a plurality of remote communication devices 16 (remote communication device 16A, remote communication device 16B, and remote communication device 16C).

[0014] The base communication device 14 is a device provided in industrial equipment including industrial machinery such as machine tools. The base communication device 14 may be provided in a numerical control device 18 that controls the industrial machinery. In this case, the base communication device 14 may be configured integrally with the numerical control device 18. In other words, the base communication device 14 may be provided as the numerical control device 18.

[0015] The remote communication device 16 is a device that communicates with the base communication device 14. The remote communication device 16 is provided in, for example, an electronic device, equipment, or the like controlled by the above-mentioned numerical control device 18. More specifically, the remote communication device 16 is provided in, for example, each of a plurality of servo amplifiers 20 controlled by the numerical control device 18. In this case, the servo amplifier 20 drives a motor (servo motor) (not shown) based on a command given from the numerical control device 18 via the base communication device 14 and the remote communication device 16. The motor may be provided in, for example, the above-mentioned industrial machine. The servo amplifier 20 and the remote communication device 16 may be configured integrally. In other words, the remote communication device 16 may be provided as the servo amplifier 20.

[0016] A remote communication device 16 can be connected downstream of the base communication device 14, for example, via a connector or transmission cable (not shown). Another remote communication device 16 can be connected downstream of the remote communication device 16, for example, via a connector or transmission cable (not shown). In other words, a plurality of remote communication devices 16 can be connected sequentially downstream of the base communication device 14. As a result, the plurality of communication devices 12 form a transmission path 22 for realizing serial data communication.

[0017] The base communication device 14 and the remote communication device 16 can transmit and receive communication packets 24 via a transmission path 22. In the following, unless otherwise specified, the case where the communication packet 24 is transmitted from the base communication device 14 to the remote communication device 16 will be mainly described.

[0018] FIG. 2 is a block diagram of a base communication device 14 of the plurality of communication devices 12.

[0019] As shown in FIG. 2, the base communication device 14 includes a storage unit 26 (storage unit 26B) and a calculation unit 28 (calculation unit 28B).

[0020] The storage unit 26B includes one or more memories. The one or more memories include non-volatile memories. The non-volatile memories are recording media that non-temporarily store programs (computer programs), tables, maps, etc. For example, non-volatile memories include ROM (Read Only Memory) and flash memory. The storage unit 26B (one or more memories) may include volatile memories. For example, volatile memories include RAM (Random Access Memory).

[0021] The calculation unit 28B includes a predetermined processing circuit (not shown). The processing circuit includes one or more processors, such as a central processing unit (CPU) or a graphics processing unit (GPU). The processing circuit may include a predetermined integrated circuit, such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA).

[0022] The calculation unit 28B includes a synchronization signal generation unit 30 (base synchronization signal generation unit 30B), a communication processing unit 32 (base communication processing unit 32B), and a timing correction unit 34 (base timing correction unit 34B). The base synchronization signal generation unit 30B, the base communication processing unit 32B, and the base timing correction unit 34B are realized by the calculation unit 28B (processor) executing a program stored in the storage unit 26B (memory). At least some of the base synchronization signal generation unit 30B, the base communication processing unit 32B, and the base timing correction unit 34B may be realized by a predetermined integrated circuit such as the ASIC or FPGA provided in the calculation unit 28B.

[0023] The synchronization signal generating unit 30 generates a synchronization signal S (see also Figures 3A and 6A to 6C). The synchronization signal S is, for example, a binary signal. The ON state of the synchronization signal S, which is a binary signal, is maintained for a predetermined rise time TR. The length of the rise time TR is, for example, an integer multiple of the period of the clock of the above-mentioned processor. The synchronization signal generating unit 30 can periodically generate the synchronization signal S, for example, based on the frequency of the clock of the above-mentioned processor. The base synchronization signal generating unit 30B is a synchronization signal generating unit 30 provided in the base communication device 14. In the following description, the synchronization signal S generated by the base synchronization signal generating unit 30B will also be referred to as the base synchronization signal S.

[0024] The communication processing unit 32 executes communication processing in the communication device 12. The communication processing unit 32 can periodically execute communication processing based on the timing of the synchronization signal S. The base communication processing unit 32B is a communication processing unit 32 provided in the base communication device 14. The base communication processing unit 32B can periodically execute communication processing in the base communication device 14 based on the above-mentioned base synchronization signal S. The communication processing unit 32 includes a data receiving unit 36 ​​(base data receiving unit 36B), a data processing unit 38 (base data processing unit 38B), and a data transmitting unit 40 (base data transmitting unit 40B).

[0025] The data receiving unit 36 ​​receives communication data transmitted to the communication processing unit 32. The communication data reception process by the data receiving unit 36 ​​is included in the communication process described above. The base data receiving unit 36B is the data receiving unit 36 ​​provided in the base communication processing unit 32B. Therefore, the base data receiving unit 36B receives communication data transmitted to the base communication processing unit 32B.

[0026] The communication data received by the base data receiving unit 36B includes, for example, a correction command (timing signal). The correction command is an external command for correcting the timing of the above-mentioned base synchronization signal S. The communication data including the correction command is transmitted, for example, from an electronic device (not shown) other than the numerical control device 18 in which the base communication device 14 is provided, in order to synchronize the numerical control device 18 with the other electronic device. The other electronic device is, for example, a numerical control device other than the numerical control device 18 in which the base communication device 14 is provided, but is not limited to this.

[0027] The data processing unit 38 performs predetermined data processing based on the communication data received by the data receiving unit 36. The predetermined data processing by the data processing unit 38 may be included in the above-mentioned communication processing. The base data processing unit 38B is the data processing unit 38 provided in the base communication processing unit 32B.

[0028] The base data processing unit 38B acquires information indicating the correction command, for example, based on the communication data received by the base data receiving unit 36B. The base data processing unit 38B also generates a communication packet 24 to be transmitted to the remote communication device 16A connected downstream of the base communication device 14.

[0029] The communication packet 24 has a bit string (plurality of bit data). As shown in FIG. 1, the communication packet 24 has a start code storage section 50 and a data storage section 52. A start code SC is stored in the start code storage section 50 by the base data processing section 38B. The start code SC indicates the leading portion of the communication packet 24 in serial data communication. When the communication packet 24 is transmitted, the start code SC of the communication packet 24 is transmitted first.

[0030] The data storage unit 52 stores data that is sequentially transmitted after the start code SC. The data storage unit 52 has a portion where correction-related data 54 is stored. A more detailed description of the correction-related data 54 will be given later. The correction-related data 54 transmitted from the base communication device 14 is preferably stored relatively close to the beginning of the data storage unit 52. For example, it is preferable that the correction-related data 54 be located at the beginning of the data storage unit 52 (FIG. 1).

[0031] The data storage unit 52 also stores command data 56 addressed to the remote communication device 16. For example, as shown in FIG. 1 , the remote communication device 16A, the remote communication device 16B, and the remote communication device 16C are sequentially connected downstream of the base communication device 14. In this case, the base data processing unit 38B stores multiple pieces of command data 56 (command data 56A, command data 56B, and command data 56C) in the data storage unit 52 of the communication packet 24 (communication packet 241) transmitted from the base communication device 14. The command data 56A is the command data 56 addressed to the remote communication device 16A. The command data 56A includes, for example, a command from the numerical control device 18 to the servo amplifier 20 (servo amplifier 20A) equipped with the remote communication device 16A. The command data 56B is the command data 56 addressed to the remote communication device 16B. The command data 56B includes, for example, a command from the numerical control device 18 to the servo amplifier 20 (servo amplifier 20B) equipped with the remote communication device 16B. The command data 56C is command data 56 addressed to the remote communication device 16C. The command data 56C includes, for example, a command from the numerical control device 18 to the servo amplifier 20 (servo amplifier 20C) equipped with the remote communication device 16C.

[0032] The order of the multiple command data 56 in the communication packet 24 may be determined based on the order of the multiple remote communication devices 16 along the transmission path 22. In this case, it is preferable that the command data 56 addressed to one remote communication device 16 is located closer to the end of the communication packet 24 than the command data 56 addressed to another remote communication device 16 located downstream of the one remote communication device 16. In other words, it is preferable that the command data 56 addressed to one remote communication device 16 is stored in front (at the beginning) of the command data 56 addressed to the other remote communication device 16 located downstream of the one remote communication device 16. For example, it is preferable that the command data 56B addressed to the remote communication device 16B is stored in front of the command data 56A addressed to the remote communication device 16A.

[0033] The data transmitting unit 40 transmits a communication packet 24 to another communication device 12 connected downstream of the communication device 12. The process of transmitting the communication packet 24 by the data transmitting unit 40 is included in the communication process described above. The base data transmitting unit 40B is a data transmitting unit 40 provided in the base communication processing unit 32B. The base data transmitting unit 40B transmits a communication packet 241 to a remote communication device 16A connected downstream of the base communication device 14.

[0034] The timing correction unit 34 executes a timing correction process. The timing correction process corrects the timing of the synchronization signal S. The timing correction unit 34 shifts the timing at which the synchronization signal S switches from an OFF state to an ON state by k clocks (k: an integer), for example, based on the processor clock. In this way, the timing correction unit 34 corrects the timing of the synchronization signal S. The base timing correction unit 34B is a timing correction unit 34 provided in the base communication device 14. The base timing correction unit 34B corrects the timing of the base synchronization signal S, for example, based on a correction command received by the base data receiving unit 36B. The processing circuit (calculation unit 28B) provided in the base communication device 14 (numerical control device 18) may also generate a synchronization signal separate from the synchronization signal S. The separate synchronization signal may be, for example, a signal (binary signal) used to time various processes other than the communication process by the base communication device 14 (numerical control device 18). For example, the timing of the separate synchronization signal may be misaligned with the timing of the synchronization signal S due to clock deviation. In this case, the base timing correction unit 34B may correct the timing of the synchronization signal S so that the synchronization signal S is synchronized with the other synchronization signal. For example, the base timing correction unit 34B may change the timing of the synchronization signal S so that it matches the timing of the other synchronization signal.

[0035] Fig. 3A is a timing chart showing a simplified example of the timing of the synchronization signal S. Fig. 3B is a timing chart showing a simplified example of the timing of the synchronization signal S after correction when the synchronization signal S is corrected. For comparison, the dashed line in Fig. 3B shows the synchronization signal S when no correction is performed.

[0036] The reference time t0 in FIG. 3A indicates, for example, one timing at which the synchronization signal S is turned off. In contrast, the time ta shown in FIG. 3A is the timing at which the synchronization signal S is turned on again after the reference time t0. If the timing correction unit 34 performs timing correction processing by time t0, the synchronization signal S is turned on at a time tb different from time ta, as shown in FIG. 3B, for example. The rise time TR is not changed before and after the timing correction processing. Note that while FIG. 3B shows a case in which the timing of the synchronization signal S is advanced, the timing correction unit 34 may also delay the timing of the synchronization signal S. Furthermore, although FIG. 3B shows the timing at which the synchronization signal S is turned off after correction coincides with time ta (ta - tb = TR), this is not limiting.

[0037] Information indicating the amount of correction of the base synchronization signal S by the base timing correction unit 34B is stored in the data storage unit 52 of the communication packet 241 as the above-mentioned correction-related data 54. This allows the base data transmission unit 40B to transmit the communication packet 241 including the correction-related data 54 to the remote communication device 16A. Note that if there is no need to correct the timing of the base synchronization signal S, information indicating that the amount of correction is zero (no correction) may be stored in the data storage unit 52 as the correction-related data 54.

[0038] The base data transmitter 40B may periodically transmit the communication packets 24 based on the base synchronization signal S. That is, after transmitting one communication packet 241 in one processing cycle, the base data transmitter 40B may transmit another communication packet 241 in the processing cycle following the one processing cycle. In consideration of this, the base timing corrector 34B performs timing correction processing in accordance with the correction-related data 54 included in one communication packet 241 from the start of transmission of the one communication packet 241 to the start of transmission of the other communication packet 241. For example, the base timing corrector 34B performs timing correction processing in accordance with the correction-related data 54 stored in the one communication packet 241 during the processing cycle in which the base data receiver 36B performed transmission processing of the one communication packet 241. In this case, the transmission timing of the one communication packet 241 is determined based on the synchronization signal S before correction. In contrast, the transmission timing of the other communication packets 241 is determined based on the synchronization signal S after correction (the correction amount).

[0039] FIG. 4 is a block diagram of a remote communication device 16 of the plurality of communication devices 12.

[0040] The remote communication device 16 includes a storage unit 26 (storage unit 26R) and a calculation unit 28 (calculation unit 28R).

[0041] The storage unit 26R includes one or more memories. The one or more memories include non-volatile memories. Non-volatile memories are recording media that non-temporarily store programs, tables, maps, etc. For example, ROM, flash memory, etc. are included in non-volatile memories. The storage unit 26R (one or more memories) may also include volatile memories. For example, RAM is included in volatile memories.

[0042] The calculation unit 28R includes a predetermined processing circuit (not shown). The processing circuit includes, for example, one or more processors such as a CPU, a GPU, etc. The processing circuit may also include a predetermined integrated circuit such as an ASIC, an FPGA, etc.

[0043] The calculation unit 28R includes a synchronization signal generation unit 30 (remote synchronization signal generation unit 30R), a communication processing unit 32 (remote communication processing unit 32R), and a timing correction unit 34 (remote timing correction unit 34R). The calculation unit 28R also includes a comparison unit 42. The remote synchronization signal generation unit 30R, the remote communication processing unit 32R, the remote timing correction unit 34R, and the comparison unit 42 are realized by the calculation unit 28R (processor) executing a program stored in the storage unit 26R (memory). At least some of the remote synchronization signal generation unit 30R, the remote communication processing unit 32R, the remote timing correction unit 34R, and the comparison unit 42 may be realized by a predetermined integrated circuit such as the ASIC or FPGA provided in the calculation unit 28R.

[0044] The remote synchronization signal generating unit 30R is a synchronization signal generating unit 30 provided in the remote communication device 16. In the following description, the synchronization signal S generated by the remote synchronization signal generating unit 30R will also be referred to as the remote synchronization signal S.

[0045] The remote communication processing unit 32R is the communication processing unit 32 provided in the remote communication device 16. The remote communication processing unit 32R can periodically execute communication processing in the remote communication device 16 based on the above-mentioned remote synchronization signal S. The communication processing unit 32 includes a data receiving unit 36 ​​(remote data receiving unit 36R), a data processing unit 38 (remote data processing unit 38R), and a data transmitting unit 40 (remote data transmitting unit 40R).

[0046] The remote data receiving unit 36R is the data receiving unit 36 ​​provided in the remote communication processing unit 32R. The remote data receiving unit 36R receives communication data transmitted to the remote communication processing unit 32R. In this case, the communication data includes the above-mentioned communication packet 24 (communication packet 241).

[0047] The communication packet 24 received by the remote data receiving unit 36R is transmitted from the communication device 12 disposed upstream of the remote communication device 16 including the remote data receiving unit 36R. For example, the remote data receiving unit 36R of the remote communication device 16A receives a communication packet 241 transmitted from the base communication device 14. Also, for example, the remote data receiving unit 36R of the remote communication device 16B receives the communication packet 24 transmitted from the remote communication device 16A. The remote data receiving unit 36R of the remote communication device 16C receives the communication packet 24 transmitted from the remote communication device 16B.

[0048] The remote data processing unit 38R is the data processing unit 38 included in the remote communication processing unit 32R. The remote data processing unit 38R acquires, for example, command data 56 addressed to the remote communication device 16 including the remote data processing unit 38R, from the communication packet 24 received by the remote data receiving unit 36R. The remote data processing unit 38R also acquires correction-related data 54 stored in the data storage unit 52 of the communication packet 24.

[0049] Furthermore, the remote data processing unit 38R generates a communication packet 24 to be transmitted to another remote communication device 16 that is disposed downstream of the remote communication device 16 that includes the remote data processing unit 38R. In this case, the remote data processing unit 38R stores a forwarded data group 58 in the data storage unit 52 of the communication packet 24 transmitted from the remote communication device 16.

[0050] The forwarded data group 58 includes, for example, return data 60. The return data 60 is data sent from the remote communication device 16 (servo amplifier 20) to the base communication device 14 (numerical control device 18). The return data 60 includes, for example, feedback information that is fed back from the servo amplifier 20 to the numerical control device 18 regarding the control of a servo motor by the numerical control device 18. The return data 60 is preferably stored relatively close to the beginning of the data storage unit 52 (see also FIG. 1).

[0051] The remote data processing unit 38R of the remote communication device 16A stores return data 60A sent from the remote communication device 16A (servo amplifier 20A) to the base communication device 14 (numerical control device 18) in the data storage unit 52. The remote data processing unit 38R of the remote communication device 16B stores return data 60B sent from the remote communication device 16B (servo amplifier 20B) to the base communication device 14 (numerical control device 18) in the data storage unit 52.

[0052] The forwarded data group 58 also stores data corresponding to the contents of the communication packet 24 received by the remote communication device 16. For example, the forwarded data group 58 may include one or more pieces of return data 60 stored in the communication packet 24 received by the remote communication device 16 and the correction-related data 54.

[0053] Furthermore, the forwarded data group 58 may include the command data 56 stored in the communication packet 24 received by the remote data receiving unit 36R. However, when a communication packet 24 is received by a remote communication device 16, the command data 56 addressed to that remote communication device 16 does not have to be included in the forwarded data group 58 of the communication packet 24 transmitted from that remote communication device 16. In other words, the command data 56 addressed to a certain remote communication device 16 does not have to be forwarded to another remote communication device 16 arranged downstream of that remote communication device 16. For example, the command data 56A addressed to the remote communication device 16A does not have to be stored in the data storage unit 52 of the communication packet 24 transmitted from the remote communication device 16A. Similarly, the command data 56B addressed to the remote communication device 16B does not have to be stored in the data storage unit 52 of the communication packet 24 transmitted from the remote communication device 16B.

[0054] The remote data transmission unit 40R is a data transmission unit 40 provided in the remote communication processing unit 32R. The remote data transmission unit 40R transmits a communication packet 24 to another remote communication device 16 connected in a subsequent stage to the remote communication device 16.

[0055] In order to speed up communication, it is preferable that the transmission process for transmitting the start code SC of the communication packet 24 be started before the estimated reception timing. The estimated reception timing is the timing at which the communication packet 24 is estimated to arrive at the remote data receiving unit 36R. More specifically, the estimated reception timing is the timing at which the start code SC transmitted from the previous stage is expected to arrive at the remote data receiving unit 36R. The estimated reception timing can be determined in advance based on the remote synchronization signal S.

[0056] The remote data transmitter 40R starts transmitting the communication packet 24 (start code SC) to the subsequent stage, regardless of whether the remote data receiver 36R has received the communication packet 24 (start code SC). As a result, the start code SC corresponding to the forwarded data group 58 may be transmitted before the forwarded data group 58 corresponding to the communication packet 24 received by the remote data receiver 36R is generated. The forwarded data group 58 corresponding to the start code SC to be transmitted in this case is sequentially generated by the remote data processor 38R when the communication packet 24 is received by the remote data receiver 36R. The generated forwarded data group 58 is then sequentially transmitted by the remote data transmitter 40R. The remote data processor 38R (remote communication device 16) may obtain feedback information from the servo amplifier 20 in which the remote communication device 16 is provided. In this case, the remote data processor 38R of the remote communication device 16 may generate a portion of the forwarded data group 58 based on the feedback information without waiting for the communication packet 24 to be transmitted from the previous stage. A part of the forwarded data group 58 may be transmitted sequentially following the start code SC without waiting for the remaining part of the forwarded data group 58 to be generated.

[0057] The comparator 42 compares the reception timing of the communication packet 24 by the remote data receiver 36R with the estimated reception timing. The comparison result by the comparator 42 indicates the amount of deviation between the remote synchronization signal S of the remote communication device 16 in which the comparator 42 is provided and the synchronization signal S of the communication device 12 arranged upstream of the remote communication device 16. For example, the comparison result by the comparator 42 provided in the remote communication device 16A indicates the amount of deviation between the remote synchronization signal S of the remote communication device 16A and the base synchronization signal S.

[0058] 5 is a table showing the relationship between the deviation correction amount CAa specified by the comparison result (comparison result) by the comparator 42, the tracking correction amount CAb specified by the correction-related data 54, and the combined correction amount CAc obtained by combining the deviation correction amount CAa and the tracking correction amount CAb. Note that a plus sign in FIG. 5 conveniently indicates a correction amount that delays the timing of the synchronization signal S. Conversely, a minus sign in FIG. 5 conveniently indicates a correction amount that advances the timing of the synchronization signal S.

[0059] The remote timing correction unit 34R is a timing correction unit 34 provided in the remote communication device 16. The remote timing correction unit 34R performs timing correction processing in accordance with correction-related data 54 included in one communication packet 24 before another communication packet 24 transmitted after the one communication packet 24 is received by the remote data receiving unit 36R. For example, the remote timing correction unit 34R performs timing correction processing in accordance with the correction-related data 54 stored in one communication packet 24 during the processing cycle in which the remote data receiving unit 36R performs reception processing for the one communication packet 24. In this case, the correction amount of the remote synchronization signal S by the remote timing correction unit 34R is specified as a total correction amount CAc as shown in FIG. 5. That is, the remote timing correction unit 34R specifies a deviation correction amount CAa, which is a correction amount for correcting the deviation amount, based on the comparison result by the comparing unit 42 described above. The remote timing correction unit 34R also determines a tracking correction amount CAb based on the correction-related data 54 acquired by the remote communication processing unit 32R (remote data processing unit 38R). In this case, the tracking correction amount CAb is the amount of correction of the base synchronization signal S by the base communication device 14. The remote timing correction unit 34R adds together the deviation correction amount CAa and the tracking correction amount CAb to determine a total correction amount CAc (CAc = CAa + CAb). The remote timing correction unit 34R corrects the timing of the remote synchronization signal S of the remote communication device 16 that includes the remote timing correction unit 34R based on the total correction amount CAc.

[0060] 5, the total correction amount CAc may be zero. In this case, the remote timing correction unit 34R maintains the timing of the remote synchronization signal S that has already been set.

[0061] According to the above-described communication system 10, for example, the following advantageous effects can be achieved.

[0062] The communication system 10 includes a plurality of communication devices 12. A first communication device 12, which is one of the plurality of communication devices 12, transmits a communication packet 24 to a second communication device 12, which is another of the plurality of communication devices 12. In this case, the first communication device 12 and the second communication device 12 are, for example, the base communication device 14 and the remote communication device 16A connected downstream of the base communication device 14, respectively. The communication processing unit 32 (first communication processing unit 32) of the first communication device 12 can include correction-related data 54, which is data related to correction of the synchronization signal S, in the communication packet 24 and transmit the communication packet 24 to the communication processing unit 32 (second communication processing unit 32) of the second communication device 12. The correction-related data 54 indicates, for example, a correction amount (first correction amount) of the synchronization signal S (first synchronization signal S1) in the first communication device 12.

[0063] The timing correction unit 34 (first timing correction unit 34) of the first communication device 12 executes timing correction processing (first timing correction processing) according to the correction-related data 54 included in one communication packet 24. The first timing correction unit 34 executes the first timing correction processing described above after transmission of the one communication packet 24 is started. Furthermore, the first timing correction unit 34 completes the first timing correction processing before transmission of another communication packet 24, which is to be transmitted from the first communication device 12 after the one communication packet 24, to the second communication device 12 is started. As a result, the first synchronization signal S1 is corrected after the transmission processing for transmitting the one communication packet 24 is started and before the transmission processing for transmitting the other communication packet 24 is started. As a result, the one communication packet 24 is transmitted at a timing based on the first synchronization signal S1 before correction, and the other communication packet 24 is transmitted at a timing based on the first synchronization signal S1 after correction.

[0064] In addition, the timing correction unit 34 (second timing correction unit 34) of the second communication device 12 performs timing correction processing (second timing correction processing) based on correction-related data 54 contained in one communication packet 24 received by the second communication processing unit 32.

[0065] 6A to 6D are diagrams showing a timing chart of the synchronization signal S (first synchronization signal S1) in the first communication device 12 and a timing chart of the synchronization signal S (second synchronization signal S2) in the second communication device 12, which are shown in parallel. The time t0 and the time ta correspond to those in FIGS. 3A and 3B.

[0066] The first synchronization signal S1 and the second synchronization signal S2 shown in FIG. 6A are synchronized. In this case, both the first synchronization signal S1 and the second synchronization signal S2 are turned off at time t0 and then turned on again at time ta. If the timing of the first synchronization signal S1 is corrected by time t0, the first synchronization signal S1 is turned on at time tb, which is different from time ta (FIG. 6B). Here, when the first communication device 12 performs a timing correction process, it includes correction-related data 54 corresponding to the timing correction process in a communication packet 24 transmitted based on the timing before correction and transmits the packet to the second communication device 12. This allows the second communication device 12 to perform a timing correction process in conjunction with the timing correction process performed by the first communication device 12 (FIG. 6B). As a result, synchronization between the first synchronization signal S1 and the second synchronization signal S2 can be maintained.

[0067] As described above, according to the present embodiment, the second communication device 12 can recognize in advance the amount of change in the transmission timing of another communication packet 24 to be transmitted after one communication packet 24, based on the correction-related data 54 included in the one communication packet 24. The second communication device 12 corrects the timing of the second synchronization signal S2 in accordance with the correction of the timing of the first synchronization signal S1, thereby suppressing misalignment between the first synchronization signal S1 and the second synchronization signal S2.

[0068] Furthermore, the second communication device 12, which is the remote communication device 16, includes a comparison unit 42. The comparison unit 42 compares the reception timing with the estimated reception timing. The correction amount of the second synchronization signal S2 by the second timing correction unit 34 (the above-mentioned total correction amount CAc) is determined based on the comparison result by the comparison unit 42 and the above-mentioned correction-related data 54. This allows the second communication device 12 to satisfactorily synchronize the second synchronization signal S2 with the first synchronization signal S1 even when the first synchronization signal S1 and the second synchronization signal S2 are out of sync due to clock deviation.

[0069] For example, as shown in FIGS. 6C and 6D, the second synchronization signal S2 may be delayed relative to the first synchronization signal S1, and then the first synchronization signal S1 may be corrected to be delayed. When the delay amount (tc-ta) of the second synchronization signal S2 relative to the first synchronization signal S1 is equal to the correction amount of the first synchronization signal S1, this corresponds to, for example, pattern 6 in FIG. 5. In this case, the total correction amount CAc is zero, so the second timing correction unit 34 does not change the timing of the second synchronization signal S2. That is, as shown in FIG. 6D, only the timing of the first synchronization signal S1 is corrected between the first synchronization signal S1 and the second synchronization signal S2. As a result, the first synchronization signal S1 and the second synchronization signal S2 may be synchronized.

[0070] The second communication processing unit 32 also transmits a communication packet 24 to a third communication device 12 among the multiple communication devices 12. The third communication device 12 is, for example, a remote communication device 16B that is disposed downstream of the remote communication device 16A, which is the second communication device 12. The communication packet 24 transmitted from the second communication processing unit 32 to the third communication device 12 also includes correction-related data 54. In this case, the correction-related data 54 may be included in the forwarded data group 58. The third communication device 12 may correct the synchronization signal S in the third communication device 12 based on the communication packet 24 (correction-related data 54) received from the second communication device 12. In this manner, not only the second communication device 12 but also the third communication device 12 can perform timing correction processing according to the correction amount (first correction amount) of the synchronization signal S indicated by the correction-related data 54.

[0071] The second communication processing unit 32 may start the transmission process for transmitting the start code SC of the communication packet 24 before the estimated reception timing. In other words, the second communication processing unit 32 may transmit the start code SC of a communication packet 24 corresponding to a communication packet 24 to the third communication device 12 without receiving the start code SC of the communication packet 24 transmitted from the first communication device 12. Because the start code SC is standard data (standard bit string), it can be generated without referring to the contents of the communication packet 24. Therefore, the second communication processing unit 32 can transmit the start code SC to the third communication device 12 without waiting for the communication packet 24 transmitted from the first communication device 12. The forwarding data group 58 to be transmitted following the start code SC is sequentially generated and transmitted. In this way, the transmission process and the reception process are partially executed in parallel without interrupting the communication packet 24. In other words, excellent communication (serial data communication) can be achieved in terms of time efficiency.

[0072] The storage location of the correction-related data 54 in the communication packet 24 transmitted from the base communication device 14 is preferably between the start code SC and the command data 56. In other words, the storage location of the correction-related data 54 in the communication packet 24 is preferably higher than the storage location of the command data 56 in the communication packet 24. This reduces the time from when the start code SC is received by the remote communication device 16 until the base communication device 14 receives the correction-related data 54. As a result, the remote communication device 16 that receives the start code SC can perform timing correction processing based on the correction-related data 54 as quickly as possible. Note that the above-mentioned comparison unit 42 can derive the comparison result when the start code SC is received by the remote communication device 16 that includes the comparison unit 42. Therefore, the remote communication device 16 that receives the start code SC can perform timing correction processing based on the comparison result by the comparison unit 42 and the correction-related data 54 as quickly as possible.

[0073] As described above, a communication packet 24 may contain multiple pieces of command data 56 addressed to multiple remote communication devices 16. The storage location of the command data 56 addressed to one remote communication device 16 in the communication packet 24 is preferably closer to the end than the storage location of the command data 56 addressed to another remote communication device 16 located downstream of the one remote communication device 16. This allows the one remote communication device 16 to receive the command data 56 to be forwarded to a downstream device of the one remote communication device 16 earlier than the command data 56 addressed to the one remote communication device 16. As a result, the one remote communication device 16 can forward the command data 56 to be forwarded to a downstream device of the one remote communication device 16 as quickly as possible. This reduces the time between when the communication packet 24 is transmitted from the base communication device 14 and when the remote communication device 16 located at the end of the transmission path 22 receives the command data 56. That is, good communication (serial data communication) can be achieved in terms of time efficiency. Moreover, even in this case, each of the multiple remote communication devices 16 can execute a part of the receiving process and the transmitting process in parallel, as described above. Therefore, for example, the deviation between the timing at which the remote communication device 16A acquires the command data 56A, the timing at which the remote communication device 16B acquires the command data 56B, and the timing at which the remote communication device 16C acquires the command data 56C can be suppressed. As a result, for example, multiple servo amplifiers 20 can be synchronized.

[0074] Comparative Example To aid in understanding the above-described embodiment, a comparative example will be described below. Fig. 7 is a configuration diagram of a communication system 100 according to the comparative example.

[0075] The communication system 100 includes a plurality of communication devices 120. The plurality of communication devices 120 includes a base communication device 140 and a plurality of remote communication devices 160 (remote communication device 160A, remote communication device 160B, and remote communication device 160C) connected in sequence downstream of the base communication device 140. The base communication device 140 corrects the timing of a synchronization signal S in the base communication device 140 based on a timing signal input from outside. The base communication device 140 also transmits a communication packet 24 to the remote communication device 160. However, the communication packet 24 transmitted from the base communication device 140 does not store correction-related data 54.

[0076] 8 is a diagram showing, in parallel, a timing chart of the synchronization signal S (synchronization signal SBX) in the base communication device 140 according to the comparative example and a timing chart of the synchronization signals S (synchronization signals SRX1 and SRX2) in multiple remote communication devices 160. The synchronization signal SRX1 is the synchronization signal S of the remote communication device 160A. The synchronization signal SRX2 is the synchronization signal S of the remote communication device 160B.

[0077] At time t1, the synchronization signal SBX, the synchronization signal SRX1, and the synchronization signal SRX2 are synchronized. Thereafter, the base communication device 140 executes a timing correction process based on, for example, an external timing signal. This corrects the timing of the synchronization signal SBX. However, as described above, the correction-related data 54 is not stored in the communication packet 24 transmitted from the base communication device 140. Therefore, even if the remote communication device 160 receives the communication packet 24 from the base communication device 140, it cannot recognize that the base communication device 140 is executing the timing correction process. As a result, the timing at which the synchronization signal SRX1 is turned on (time t2) differs from the timing at which the corrected synchronization signal SBX is turned on.

[0078] If the above-described comparison unit 42 is provided in the remote communication device 160, the timing correction process in the remote communication device 160 may be performed based on the comparison result by the comparison unit 42. However, it is not necessarily preferable for each of the multiple remote communication devices 160 to perform the timing correction process based solely on the comparison result by the comparison unit 42. The reason for this is as follows.

[0079] If the remote communication device 160A is equipped with a comparison unit 42, the remote communication device 160A can perform timing correction processing based on the comparison result between the reception timing of the start code SC transmitted from the base communication device 140 and the estimated reception timing. However, the remote communication device 160A recognizes the difference between the reception timing and the estimated reception timing only after the remote communication device 160A receives the start code SC transmitted from the base communication device 140 based on the corrected synchronization signal SBX. In other words, the remote communication device 160A recognizes the difference between the reception timing and the estimated reception timing only after time t2. In this case, the base communication device 140 and the multiple remote communication devices 160 become at least temporarily out of sync.

[0080] Furthermore, the remote communication device 160A may transmit the start code SC to the remote communication device 160B before receiving the start code SC transmitted from the base communication device 140. In this case, the remote communication device 160B receives the start code SC transmitted by the remote communication device 160A before the remote communication device 160A performs the timing correction process. Therefore, the remote communication device 160B cannot recognize, based on the reception timing of the start code SC, that the remote communication device 160A is performing the timing correction process. The remote communication device 160B recognizes the discrepancy between the reception timing and the estimated reception timing only after the remote communication device 160B receives the start code SC transmitted from the remote communication device 160A based on the corrected synchronization signal SRX1. In other words, the remote communication device 160B recognizes the discrepancy between the reception timing and the estimated reception timing after time t3, which is later than time t2. In this case, the asynchronous state between the base communication device 140 and the multiple remote communication devices 160 will not be resolved until time t4 when the result of the timing correction process executed by the remote communication device 160B after time t3 is reflected.

[0081] As described above, the communication system 100 according to the comparative example cannot necessarily effectively prevent the plurality of communication devices 120 from falling into an asynchronous state. In contrast, the communication system 10 according to the above-described embodiment can effectively prevent the plurality of communication devices 120 from falling into an asynchronous state. Therefore, the communication system 10 according to the embodiment can achieve good communication.

[0082] One embodiment may be modified as follows. In the following modifications, descriptions that overlap with the embodiment will be omitted as appropriate. In addition, in the drawings used in the following modifications, the same reference numerals are used for the same components as those described in the embodiment.

[0083] (Variation 1) The remote data processing unit 38R generates a communication packet 24 addressed to another remote communication device 16 arranged downstream of the remote communication device 16 including the remote data processing unit 38R (see one embodiment). In this case, the remote data processing unit 38R may store data indicating the total correction amount CAc (second correction amount) in the communication packet 24 as new correction-related data 54. In this case, the total correction amount CAc is determined by the remote timing correction unit 34R of the remote communication device 16 including the remote data processing unit 38R.

[0084] For example, the remote communication device 16A transmits a communication packet 24 to the remote communication device 16B. Data indicating the total correction amount CAc specified by the remote data processing unit 38R of the remote communication device 16A may be stored in the communication packet 24 as new correction-related data 54. In this case, the remote communication device 16B can correct the timing of the remote synchronization signal S of the remote communication device 16B based on the total correction amount CAc specified by the remote communication device 16A.

[0085] Furthermore, for example, the remote communication device 16B transmits a communication packet 24 to the remote communication device 16C. In this case, data indicating the total correction amount CAc specified by the remote data processing unit 38R of the remote communication device 16B may be stored in the communication packet 24 as new correction-related data 54. In this case, the remote communication device 16C can correct the timing of the remote synchronization signal S of the remote communication device 16C based on the total correction amount CAc specified by the remote communication device 16B.

[0086] It should be noted that the correction-related data 54 that the remote communication device 16 receives from a previous stage of the remote communication device 16 does not have to be transmitted to a subsequent stage of the remote communication device 16. For example, the remote communication device 16A does not have to transmit the correction-related data 54 received from the base communication device 14 to the remote communication device 16B. Similarly, for example, the remote communication device 16B does not have to transmit the correction-related data 54 received from the remote communication device 16A to the remote communication device 16C.

[0087] According to this modification, it is possible to synchronize two adjacent remote communication devices 16 along the transmission path 22. By synchronizing the two adjacent remote communication devices 16, all of the remote communication devices 16 included in the communication system 10 (FIG. 1) are synchronized as a result.

[0088] (Variation 2) The above-described first communication device 12 and second communication device 12 may be interpreted as two remote communication devices 16 adjacent to each other along the transmission path 22. For example, the remote communication device 16A may be interpreted as the first communication device 12, and the remote communication device 16B may be interpreted as the second communication device 12.

[0089] (Combination of Multiple Modifications) The multiple modifications described above may be combined as appropriate within a range that does not cause inconsistency.

[0090] According to the above embodiment and modifications, the communication system 10, the base communication device 14, and the remote communication device 16 can achieve good communication.

[0091] The following additional notes are further disclosed regarding the above embodiment.

[0092] (Supplementary Note 1) A communication system according to the present disclosure is a communication system (10) including a plurality of communication devices (12), wherein a first communication device among the plurality of communication devices includes a first communication processing unit (32) that executes communication processing, and a first timing correction unit (34) that executes a first timing correction process to correct the timing of a first synchronization signal (S1), which is a synchronization signal (S) used when the first communication processing unit executes the communication processing, and a second communication device among the plurality of communication devices includes a second communication processing unit (32) that executes the communication processing, and a first timing correction unit (34) that executes a first timing correction process to correct the timing of a second synchronization signal (S1), which is a synchronization signal (S) used when the second communication processing unit executes the communication processing. and a second timing correction unit that executes a second timing correction process to correct the timing of (S2), wherein the first communication processing unit includes correction-related data (54) related to correction of the synchronization signal in a communication packet (24) and transmits the communication packet to the second communication device, and the first timing correction unit executes the first timing correction process according to the correction-related data included in the one communication packet after transmission of the one communication packet from the first communication device to the second communication device has started and before transmission of another communication packet to be transmitted after the one communication packet has started from the first communication device to the second communication device.

[0093] (Supplementary Note 2) The communication system according to Supplementary Note 1 may be a communication system in which the second communication device further includes a comparison unit (42) that compares a reception timing at which the one communication packet is received by the second communication processing unit with an estimated reception timing of the one communication packet that is estimated in advance based on the second synchronization signal, and the second timing correction unit executes the second timing correction process based on a comparison result by the comparison unit and the correction-related data included in the one communication packet.

[0094] (Supplementary Note 3) The communication system according to Supplementary Note 1 or 2 may be a communication system in which the correction-related data included in the one communication packet transmitted from the first communication processing unit indicates a first correction amount, which is a correction amount of the first synchronization signal by the first timing correction unit.

[0095] (Supplementary Note 4) The communication system according to Supplementary Note 3 may be a communication system in which the second communication processing unit transmits a communication packet including the correction-related data indicating the first correction amount to a third communication device among the plurality of communication devices.

[0096] (Supplementary Note 5) The communication system according to Supplementary Note 3 may be a communication system in which the second communication processing unit transmits a communication packet including the correction-related data indicating a second correction amount, which is a correction amount of the second synchronization signal by the second timing correction unit, to a third communication device among the plurality of communication devices.

[0097] (Supplementary Note 6) The communication system may be one described in any one of Supplementary Notes 1 to 3, wherein the communication packet includes a start code (SC) indicating the beginning of the communication packet, a communication packet corresponding to the communication packet transmitted from the first communication device to the second communication device is transmitted from the second communication device to a third communication device among the plurality of communication devices, and the second communication processing unit starts transmitting the start code of the communication packet corresponding to the one communication packet to the third communication device without being based on reception of the start code of the one communication packet transmitted from the first communication device to the second communication device.

[0098] (Supplementary Note 7) The communication system according to any one of Supplementary Notes 1 to 6 may be a communication system in which the first communication device is a base communication device (14), and the second communication device is a remote communication device (16) located downstream of the base communication device.

[0099] (Supplementary Note 8) The communication system according to Supplementary Note 7 may be a communication system in which the base communication device is provided in a numerical control device (18) that controls a servo amplifier (20), and the remote communication device is provided in the servo amplifier.

[0100] (Supplementary Note 9) The base communication device according to the present disclosure is a base communication device (14) that communicates with a remote communication device (16), and includes a communication processing unit (32) that executes communication processing, and a timing correction unit (34) that executes timing correction processing to correct the timing of a synchronization signal (S) used when the communication processing is performed by the communication processing unit, wherein the communication processing unit includes correction-related data (54) related to correction of the synchronization signal in a communication packet (24) and transmits the communication packet to the remote communication device, and the timing correction unit executes the timing correction processing according to the correction-related data included in one communication packet after transmission of the one communication packet to the remote communication device has started and before transmission of another communication packet to the remote communication device that is to be transmitted after the one communication packet has started.

[0101] (Supplementary Note 10) The remote communication device according to the present disclosure is a remote communication device (16) that communicates with a base communication device (14), and includes a communication processing unit (32) that executes communication processing, and a timing correction unit (34) that executes timing correction processing to correct the timing of a synchronization signal (S) used when the communication processing unit performs the communication processing, wherein a communication packet (24) received by the communication processing unit from the base communication device includes correction-related data (54) related to correction of the synchronization signal, and the timing correction unit executes the timing correction processing according to the correction-related data included in one communication packet before another communication packet to be transmitted after the one communication packet is received by the communication processing unit.

[0102] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0103] REFERENCE SIGNS LIST 10...Communication system 12...Communication device (first communication device, second communication device, third communication device) 14...Base communication device 16...Remote communication device 18...Numerical control device 20...Servo amplifier 24...Communication packet 32...Communication processing section (first communication processing section, second communication processing section) 34...Timing correction section (first timing correction section, second timing correction section) 42...Comparator 54...Correction-related data S...Synchronization signal SC...Start code

Claims

1. A communication system comprising a plurality of communication devices, wherein a first communication device among the plurality of communication devices comprises: a first communication processing unit that executes communication processing; and a first timing correction unit that executes a first timing correction process to correct the timing of a first synchronization signal that is a synchronization signal used when the first communication processing unit executes the communication processing; and a second communication device among the plurality of communication devices comprises: a second communication processing unit that executes the communication processing; and a second timing correction unit that executes a second timing correction process to correct the timing of a second synchronization signal that is a synchronization signal used when the second communication processing unit executes the communication processing; and the first communication processing unit transmits correction-related data related to the correction of the synchronization signal to the second communication device by including it in a communication packet, A communication system in which the first timing correction unit performs the first timing correction process according to the correction-related data included in one communication packet after transmission of the one communication packet from the first communication device to the second communication device has started and before transmission of another communication packet to be transmitted after the one communication packet has started from the first communication device to the second communication device.

2. A communication system as claimed in claim 1, wherein the second communication device further comprises a comparison unit that compares the reception timing at which the one communication packet is received by the second communication processing unit with an estimated reception timing of the one communication packet that is estimated in advance based on the second synchronization signal, and the second timing correction unit executes the second timing correction process based on the comparison result by the comparison unit and the correction-related data included in the one communication packet.

3. A communication system as claimed in claim 1 or 2, wherein the correction-related data included in the one communication packet transmitted from the first communication processing unit indicates a first correction amount, which is the amount of correction of the first synchronization signal by the first timing correction unit.

4. A communication system according to claim 3, wherein the second communication processing unit transmits a communication packet including the correction-related data indicating the first correction amount to a third communication device among the plurality of communication devices.

5. A communication system according to claim 3, wherein the second communication processing unit transmits a communication packet including the correction-related data indicating a second correction amount, which is the amount of correction of the second synchronization signal by the second timing correction unit, to a third communication device among the plurality of communication devices.

6. A communication system according to any one of claims 1 to 3, wherein a communication packet includes a start code indicating the beginning of the communication packet, a communication packet corresponding to the communication packet transmitted from the first communication device to the second communication device is transmitted from the second communication device to a third communication device among the plurality of communication devices, and the second communication processing unit starts transmitting the start code of the communication packet corresponding to the one communication packet to the third communication device without being based on reception of the start code of the one communication packet transmitted from the first communication device to the second communication device.

7. A communication system according to any one of claims 1 to 6, wherein the first communication device is a base communication device, and the second communication device is a remote communication device located downstream of the base communication device.

8. A communication system according to claim 7, wherein the base communication device is provided in a numerical control device that controls a servo amplifier, and the remote communication device is provided in the servo amplifier.

9. A base communication device that communicates with a remote communication device, comprising: a communication processing unit that executes communication processing; and a timing correction unit that executes timing correction processing to correct the timing of a synchronization signal used when the communication processing is performed by the communication processing unit, wherein the communication processing unit includes correction-related data related to the correction of the synchronization signal in a communication packet and transmits the packet to the remote communication device, and the timing correction unit executes the timing correction processing according to the correction-related data included in one communication packet after transmission of the one communication packet to the remote communication device has begun and before transmission of another communication packet to the remote communication device that is to be transmitted after the one communication packet has begun.

10. A remote communication device that communicates with a base communication device, comprising: a communication processing unit that executes communication processing; and a timing correction unit that executes timing correction processing to correct the timing of a synchronization signal used when the communication processing unit performs the communication processing, wherein a communication packet received by the communication processing unit from the base communication device includes correction-related data related to the correction of the synchronization signal, and the timing correction unit executes the timing correction processing according to the correction-related data included in one communication packet before another communication packet to be transmitted after the one communication packet is received by the communication processing unit.

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