JPS639334A - Optical local area network - Google Patents

Abstract

PURPOSE:To contrive the reduction of the system cost by adopting closed loop constitution for a transmission and providing at least a couple of photoelectric conversion modules, electrooptic conversion modules and an OR circuit to a branch part to each node. CONSTITUTION:An optical signal sent through an optical fiber is converted into an electric signal by an photoelectric conversion module (O/E) at a branch part 22 to each node 14 into an electric signal, restored again into an optical signal by an electrooptic conversion module (E/O) and coupled with an optical fiber. In case, the electric signal converted at the O/E is branched into an input line to the node 14 by an OR circuit 23 and buffer amplifiers 24, 26 or a signal from the node 14 is coupled with the input of the E/O. Thus, no optical star coupler is required and the total length of the optical fiber is enough to be short.

Description

[Detailed description of the invention] Industrial application field 1 The present invention relates to a local area network.
To be more specific, the factory
This paper relates to the configuration of optical local area networks suitable for automation, etc.

BACKGROUND OF THE INVENTION FIG. 2 is a diagram schematically illustrating the configuration of a local area network for conventional FAX+J-automation using coaxial lines.

As shown in Fig. 2, a coaxial cable 10 is stretched as a bus within the factory floor, omnidirectional taps 12 are arranged at regular intervals, and a programmable controller PC is connected via an ink face bow I/F and a token bus controller TBC. The node 14 is configured by being coupled to the node 14.

Here, it is assumed that an access method called token passing bus method (compliant with IEEE802.4) will be used, and for this purpose, a token bus controller board (token bus controller board) and TBC are installed between the interface port I/F and the programmable controller PC. It is intervening.

Local area networks using such coaxial lines are (1) susceptible to noise, (2) have a narrow transmission band,
(3) Attenuation becomes a problem as the transmission distance becomes longer.

Therefore, as shown in FIG. 3, a local area network has been proposed in which the transmission medium is changed from a coaxial cable to an optical fiber 16, thereby increasing resistance to significant noise within a factory. Optical fibers are virtually unaffected by electromagnetic noise and can transmit a wide band with low attenuation.

In the optical local area network shown in FIG. 3, the transmitting and receiving optical fibers 16 from each node are coupled to an optical star coupler 18 with n inputs and n outputs, and the optical signal transmitted through the optical fibers is transmitted through the optical star coupler 18. Mixing with coupler 18
Diverted.

Problems to be Solved by the Invention In the conventional optical local area network as described above, the optical star coupler is expensive, making the entire system expensive.

In addition, when laying optical fiber cables, a star-shaped configuration centered on optical star couplers must be used, which increases the total length of the optical fiber cables used, which also causes high costs. was. Furthermore, the coupling loss of light in the optical star coupler is large, and in the current state of the art, the number of connectable nodes is limited to about 32 nodes at most.

Therefore, the present invention aims to provide an optical local area network that solves the problems of the conventional optical local area network described above.

Means for Solving the Problems According to the present invention, in a local area network in which a plurality of nodes are connected via an optical fiber transmission path, at least one pair of optical/electrical conversion modules is provided at a branch point to each node. and an electrical/optical conversion module, the optical/electrical fi conversion module receives an optical signal propagating through the optical fiber and outputs an electrical output, at least a part of which is branched to form an electrical/optical conversion module. the output of said optical/electrical conversion module is coupled to an input line to a node, and/or the output of said optical/electrical conversion module is coupled to an input line to a node, and/or the optical output of said optical/electrical conversion module is coupled to an input line to a node; Output lines are connected.

Function In an optical local area network as described above, an optical signal transmitted through an optical fiber is converted into an electrical signal by an optical/electrical conversion module at a branch point to each node, and the electrical/optical conversion module converts the optical signal back into an optical signal. and coupled into an optical fiber.

At that time, the electrical signal converted by the optical/electrical conversion module is branched to the input line to the node, or
Signals from the nodes are coupled to the input of the optical conversion module. Therefore, an optical star coupler is not required, and as many nodes as necessary can be provided. Furthermore, since the optical fiber constitutes one bus, the total length of the optical fiber cable can be shorter than that in a local area network using an optical star coupler.

Embodiments Hereinafter, embodiments of an optical local area network according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of a first embodiment of an optical local area network according to the present invention. As shown in FIG. 1, the optical fiber transmission line includes a pair of optical fibers 2OA and 2OA.
Consists of 0B. These optical fibers are provided with a branch section 22 to each node, and the branch section 22 includes two pairs of optical/electrical conversion modules 0/E shown in FIG. 1, except for the branch sections at both ends. and an electrical/optical conversion module E10. A pair of optical/electrical conversion modules 0/E and electric/optical conversion module E10 are provided at the branch portions 22 at both ends.

The branching portion 22 excluding the branching portions at both ends is constructed as shown in FIG. 4. The optical fiber 2OA is coupled to the optical/electrical conversion module ○/E, and the electrical output of the optical/electrical conversion module ○/E is connected to the input of the electrical/optical conversion module E10 via the OR circuit 22. The optical output is coupled to optical fiber 22A. And that OR
The other input of the circuit 22 is connected to the output terminal of the node's interface port ■/F. The output terminal of the interface board I/F is connected to the programmable controller P via the token bus controller TBC.
A signal is supplied from C. In this way, the optical signal from the previous branch and the signal from the node (node transmission) are
The R circuit 22 joins the electrical/optical conversion module E10.
The superimposed optical signal is output from the electrical/optical conversion module E10 to the optical fiber 2OA.

On the other hand, the optical fiber 20B is coupled to another optical/electrical conversion module O/E, and the electrical output of the optical/electrical conversion module O/E is passed through a buffer amplifier 24 for level adjustment. It is connected to the input of conversion module E10, and its optical output is coupled to optical fiber 22B. Furthermore, the output of the optical/electrical conversion module 0/E is connected to another buffer amplifier 26 for level adjustment.
interface baud) is supplied to the input terminal of the I/F. In this manner, the optical signal transmitted through the optical fiber 22B passes through the branching section via optical/electrical conversion and electrical/optical conversion, and upon optical/electrical conversion, is branched and supplied to the node.

In addition, in the optical local area network of FIG. 1, the rightmost branch is such that the output of the OR circuit 22 of FIG. 4 is directly connected to the inputs of the buffer amplifiers 24 and 26, and the leftmost branch is In this case, the input connected to the optical/electrical conversion module O/E of the OR circuit 22 in FIG. 4 is set to an open state, and the output of the buffer amplifier 24 is also set to an open state.

Thus, the pair of optical fibers 2OA and 20B have a folded structure, and the optical fiber 2O is connected to the left end branch.
The optical signal coupled to A is turned back at the right end branch, passes through the optical fiber 20B, and returns to the left end branch. In other words, the optical fibers 2OA and 20B are connected as a single system that turns back midway, and constitute a local area network in which signals are taken out or combined at branch points to each node along the way. .

In addition, in the above branch parts, the cables connecting each node and the optical/electrical conversion module O/E and the electrical/optical conversion module E/○ are shielded cables, and the housing of the branch part is sufficiently shielded. has been done.

FIG. 5 is a block diagram of a second embodiment of an optical local area network according to the present invention. In the second embodiment, the optical fiber transmission line includes one optical fiber 20 forming a closed loop.
It consists of The branch to each node is a pair of light/
An electrical conversion module O/E and an electrical/optical conversion module E10 are provided.

The connection between the optical/electric conversion module 0/E and the electric/optical conversion module E10 is configured as shown in FIG. 6, for example. That is, the optical fiber 20 is coupled to the optical/electrical conversion module O/E, and the electrical output of the optical/electrical conversion module O/E is passed through the OR circuit 22 via the buffer amplifier 24 for level adjustment. It is connected to the input of the electrical/optical conversion module E10, and its optical output is coupled to the optical fiber 20. The other input of the OR circuit 22 is connected to the output terminal of the ink face interface (I/F) of the node, and the output of the optical/electrical conversion module O/E is connected to the output terminal of the ink face output I/F of the node. The input terminal of the ink face 1/F is supplied through two buffer amplifiers 26.

In this way, the optical signal from the previous branch is photoelectrically converted by the optical/electrical conversion module O/E, and then branched and input to the node, and the signal from the node is ORed.
The signal is combined with the signal from the previous branch in the circuit and input to the electrical/optical conversion module E/○, and the superimposed optical signal is output from the electrical/optical conversion module E10 to the optical fiber 20.

Note that the propagation delay between the optical/electrical conversion module 0/E and the electrical/optical conversion module E10 is as shown in FIG. 7(a). /○ can be seen as connected with a short conductive wire. This state is equivalent to a state in which the electrical/optical conversion module E10 and the optical/electrical conversion module 0/E are optically coupled via a short optical fiber or a low spatial path, as shown in FIG. 7(b). It is. When measuring the signal rise delay t PLI (and fall delay jpHL) in such a model, it is found that the optical/electrical conversion module ○/E and the electrical/optical conversion module E10, which can be done manually at present, are
When using , the delay is about 0.1 μsec.

Also, as shown in Figures 8 and 9, the station (or node)
Equation 30, assuming that the farthest station distance Ln is 600 m, that is, the inter-station distance l is 20 m, the transmission time between the farthest stations when using an optical fiber cable and the transmission time between the farthest stations when using only a coaxial cable are as follows. They are 6 μs and 3 μs, respectively.

On the other hand, this level of difference is a little less than 10% of the expected processing time for the electronic circuit within the station, and is considered to be acceptable in terms of realizing the access method.

Furthermore, the format of the signal within the transmission medium or within the drop cable consisting of a shielded cable is a baseband signal based on a differential Manchester code, which is also standardized by IEEE 802.5.

Furthermore, from the perspective of reducing costs and improving reliability, we have developed optical/electrical conversion module ○/E and electrical/optical conversion module E/
It is desirable to convert all or part of the branch portion (Elo-0/E tap) having a circle into a hybrid RC or one-chip custom IC.

As described in detail, the optical local area network according to the present invention can realize the following effects.

■ It uses optical fiber as the transmission medium, and is advantageous for application in noisy environments such as inside factories.

■ There is no need to use expensive devices such as optical star couplers, reducing costs.

■ Compared to the system using optical star couplers, the function is similar to the number of nodes, which is advantageous in terms of reliability.

■ Compared to a method using an optical star coupler, the total length of the optical fiber cable used is shorter, resulting in cost reduction.

■ Restrictions on the number of nodes that can be connected to a network, such as in optical star cuff bras, are alleviated by adjusting the gain of the amplifier at each tap.

Therefore, the present invention is particularly useful in the field of local area networks (L to N) for factory automation (FA) using fiber optic cables. In addition, MAP (Manufacturing A
It is effective if applied to a network based on a standard communication control means for FA LAN called Automation Protocol.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a first embodiment of an optical local area network of the present invention, Fig. 2 is a block diagram of a local area network using a conventional coaxial cable, and Fig. 3 is a block diagram of a conventional optical local area network. FIG. 4 is a diagram showing a configuration example of a branch section (tap) consisting of the optical/electric conversion module 0/E and the electric/optical conversion module E10 of the present invention, and FIG. A configuration diagram of the second embodiment of the local area network, FIG. 6 shows the configuration of a branch section (tap) consisting of the optical/electrical conversion module O/E and the electrical/optical conversion module E10 of the present invention corresponding to FIG. 5. A diagram showing an example. FIG. 7 is an illustration of propagation delay in the optical/electrical conversion-electrical/optical conversion part in the local area network of the present invention. FIG. 8 is an illustration of data transmission time in the local area network according to the present invention. FIG. 9 is a graph for calculating data transmission time within a local area network according to the present invention. [Main reference numbers] 10... Coaxial cable 12... Omnidirectional tap 14... Node 16... Optical fiber 18... Optical star coupler 20. 2OA, 20B... Optical fiber 22... Branch 1/F・Interface port

Claims (4)

[Claims] (1) In a local area network that connects multiple nodes via an optical fiber transmission path, at least one pair of optical/electrical conversion module and electrical/optical conversion module is provided at the branch to each node. The conversion module receives an optical signal propagating through an optical fiber, and
outputting an electrical output, at least a portion of which is branched and supplied to an input of an electrical/optical conversion module; the optical output is coupled to an optical fiber; and the output of the optical/electrical conversion module is an input to a node. Optical local area network, characterized in that the output line from the node is coupled to the line and/or the output line from the node is coupled to the input of the electrical/optical conversion module. (2) The optical fiber transmission line is composed of a pair of optical fibers, and furthermore, two pairs of optical/electrical conversion modules and electric/optical conversion modules are provided at the branching section to each node, and the first The optical fiber is connected to a first optical/electrical conversion module at the branch point to each node, and its electrical output is connected to the first electrical/optical conversion module, and its optical output is connected to the first optical fiber. A single signal transmission system is formed in series with the first optical fiber at the branching section to each node, and the electrical output of the first optical/electrical conversion module is branched to the corresponding one. a second optical fiber connected to the input line to the node;
A second optical/electrical conversion module is connected at the branch to each node, and its electrical output is connected to the second electrical/optical conversion module, and its optical output is coupled to the second optical fiber. A single signal transmission system in series with the second optical fiber is also formed at the branch to each node, and at the input of the second electrical/optical conversion module,
The optical local area network according to claim 1, wherein an output line from the node is also coupled. (3) At the branch to the node provided at one end of the pair of optical fibers, the output of the first optical/electrical conversion module coupled to the first optical fiber is connected to the second optical fiber. Claim (2), characterized in that the module is coupled to the input of a second electrical/optical conversion module whose output is coupled to the fiber, thereby forming a folding section for a signal propagating through the optical fiber. Optical local area network described. (4) The optical fiber transmission line is composed of one optical fiber forming a closed loop, and a pair of optical/electrical conversion module and electric/optical conversion module are provided at the branching section to each node, The fiber is connected to the optical/electrical conversion module at a branch to each node, and its electrical output is connected to the electrical/optical conversion module, and its optical output is coupled to the optical fiber to each node. A single signal transmission system in series with the optical fiber is also formed at the branching section, and the electrical output of the optical/electrical conversion module is branched and connected to the input line to the node. The optical local area network according to claim 1, wherein an output line from the node is also coupled to the input of the optical conversion module.