WO2001050678A2

WO2001050678A2 - Ethernet transfer device with an embedded programmable logic controller

Info

Publication number: WO2001050678A2
Application number: PCT/US2000/033189
Authority: WO
Inventors: Richard A. Baker; Alain Marbach
Original assignee: Schneider Automation Inc.
Priority date: 1999-12-31
Filing date: 2000-12-07
Publication date: 2001-07-12
Also published as: CA2362435A1; EP1195022A2; MXPA01008829A; WO2001050678A3

Abstract

A programmable logic controller is disclosed which comprises a router having a router backplane which is connected to the programmable logic controller. The router backplane is further connected to a plurality of network ports. The programmable logic controller or network port communicates the network message to the router and the router communicates the network message only to the programmable logic controller or the network port for which the network message is intended.

Description

ETHERNET TRANSFER DEVICE WITH AN EMBEDDED PROGRAMMABLE LOGIC CONTROLLER

Technical Field This invention relates to an ethernet transfer device with an embedded programmable logic controller.

Background of the Invention

Generally, ethernet transfer controllers and programmable logic controllers (PLCs) are individually known. In the past, ethernet hubs (or

"dumb" switches) have been used in conjunction with PLCs to connect the PLC to any number of devices from which the PLC will receive network messages or to which the PLC will send network messages. However, a problem occurs when network messages are sent on the network simultaneously. When network messages are sent simultaneously, they

"collide" making the two messages unseparateable and, therefore, unintelligible to the rest of the network devices. As a result, each network device which sent a message involved in a collision must wait a random amount of time and resend the data. On a busy network, network messages may collide several times before the message successfully is sent to the intended destination. Therefore, as more devices are added to a network or when a device must send frequent messages the performance of the network is decreased, potentially to the point where data can no longer be successfully transmitted. In a network where a PLC is connected to I/O devices, many times network messages must be deterministic (i.e. arrive at their intended destination at a predictable time). If a PLC is controlling a process which must be held to a precise tolerance, a dangerous process or a process which can quickly escape required parameters is essential that the PLC have constant, deterministic and timely data regarding the process. However, traditional ethernet hubs do allow for constant, deterministic and timely due to their susceptibility to network message collisions. The present invention solves this and other problems.

Summary of the Invention

N programmable logic controller is disclosed which comprises a router having a router backplane which is connected to the programmable logic controller. The router backplane is further comiected to a plurality of network ports. The programmable logic controller or network port communicates the network message to the router and the router communicates the network message only to the programmable logic controller or the network port for which the network message is intended. The network port or programmable logic controller for which the network message is intended may comprise a plurality of network ports, a plurality of programmable logic controllers, a single network port or a single programmable logic controller.

Also disclosed is a method of transmitting a message in a programmable logic controller comprising the steps of providing a router having a router backplane, providing a programmable logic controller connected to the router backplane, providing a plurality of network ports connected to the router backplane, communicating a network message from one of the network ports or the programmable logic controller to the router, and communicating the network message from the router to only an intended destination and an apparatus for performing the method. Brief Description of the Draλvings

FIG.l is a diagram of the programmable logic controller according to the present invention.

Detailed Description of the Invention

While the invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention. It is to be understood that the present disclosure is to be considered only as an example of the principles of the invention. This disclosure is not intended to limit the broad aspect of the invention to the illustrated embodiments. The scope of protection should only be limited by the accompanying claims.

Referring to Figure 1, there is provided a device 10 for communicating messages between a programmable logic controller (PLC)

12, a plurality of network ports 14, and a router 15 with a router backplane 16. The plurality of network ports 14 and the PLC 12 generally comprise a network 17.

The PLC 12 comprises three sections: a PLC communications section 18, a PLC section 20 and a PLC backplane driver 22. The PLC 12 may be implemented either as dedicated hardware for performing its function or may be implemented as software running on a general purpose computer. The PLC communications section 18 comprises user interface necessary to control the PLC 12. The PLC section 20 processes input data about a system or process to be controlled and generates output data for controlling that system or process. The PLC backplane driver 22 receives network messages from the router 15 through the router backplane 16 and forwards the input data from the network message to the PLC section 20. The PLC backplane driver 22 also receives output data from the PLC section 20 and forwards the output data in a network message to the router 15 through the router backplane 16. While Figure 1 depicts only one PLC 12, it will be readily apparent and understood by one of ordinary skill in the art that any number of PLCs 12 could be implemented in the present device 10. Multiple PLCs 12 in the present device 10 would allow for close coupling of two PLCs 12 in a distributed control application. Optionally, instead of connecting the PLC 12 to the router backplane 16, the PLC 12 could be embedded within the router 15. However, in both instances the manner of operation remains the same. The plurality of network ports 14 each comprise an ethernet driver

24, a processing unit 26 and a network port backplane driver 28. The processing unit 26, through the ethernet driver 24 and the network backplane driver 24, receive network messages from the router 15 through the router backplane 16 and forward the network messages to an ethernet subnetwork 30 to which the ethernet driver 24 is connected. The processing unit 26 also receives network messages from the ethernet subnetwork 30 and forwards the network messages to the router 15 through the router backplane 16. The ethernet subnetwork 30 comprises at least one network device 32. N network device 32 can be a personal computer, a simple input/output device, a data relay or any other device capable of communicating on a network. As further explained below multiple network devices 32 can be implemented within an ethernet subnetwork, but the effects of the present invention are best realized when the ethernet subnetwork comprises only one network device. In operation, when the device 10 is first powered, the router 15 queries the network ports 17 and the PLCs 12 to determine a Media Access Control (MAC) address associated with every network device 32. In this manner, the router 15 knows at least the MAC address of every network device 32 to which it is comiected. Because the router 15 knows on which ethernet subdomain 30 every network device 32 is connected, when the router 15 receives a network message from one of the network ports 14 or the PLC 12, the router 15 forwards the network message only to the ethernet subdomain 30 where the message's intended destination is attached. If the router 15 receives a network message from the ethernet subdomain 30 to which the intended destination is also connected, the router 15 merely disregards the network message and does not forward it to another ethernet subdomain 30 or the PLC 12.

The message's intended destination could be all of the network ports 14 and the PLC 12, if the message was a broadcast message intended for all of the network ports 14 and PLC 12, or less than all of the network ports 14 or the PLC 12 if the network message was intended for less than all of the network ports 14 and/or PLCs 12, as is most common. In this manner, network ports 14 or PLCs 12 for which a network message was not intended do not receive the network message. As a result, network message traffic is reduced within the ethernet subdomains 30 which do not have a network device 32 which is an intended destination of the network message. Ethernet subdomains 30 which do not receive the network message, therefore, are free to transmit network messages without data collision. However, data collisions may still occur when the ethernet subdomain 30 contains more than one network device 32. Therefore, the effect of the present invention is best realized when the ethernet subdomain 30 comprises only one network device 32.

The device 10 is preferably connected to network devices 32 by electrical wires and the network messages are preferably electrical signals. However, the present invention can be easily adapted to accept fiber optical cables to connect the network devices 32 to the device 10 which transmit light pulses as the network messages. While the specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.

Claims

CLAIMSWe claim:

1. A programmable logic controller comprising: a router having a router backplane, the router backplane connected to the programmable logic controller; and a plurality of network ports connected to the router backplane wherein the programmable logic controller or network port communicates the network message to the router and the router communicates the network message only to the programmable logic controller or the network port for which the network message is intended.

2. The device of claim 1 , wherein the network port or programmable logic controller for which the network message is intended comprises a plurality of network ports.

3. The device of claim 1 , wherein the network port or programmable logic controller for which the network message is intended comprises a plurality of programmable logic controllers.

4. The device of claim 1, wherein the network port or programmable logic controller for which the network message is intended comprises a single network port.

5. The device of claim 1 , wherein the network port or programmable logic controller for which the network message is intended comprises a single programmable logic controller.

6. The device of claim 1, wherein the network port comprises a backplane driver, a processor and a network driver.

7. A programmable logic controller comprising: a router having a router backplane and a plurality of network ports wherein the programmable logic controller or network port communicates a network message to the router and the router communicates the message only to a network device for which the network message is intended.

8. The device of claim 7, wherein the network device for which the network message is intended comprises a plurality of network devices.

9. The device of claim 7, wherein the network device for which the network message is intended comprises a single network device.

10. The device of claim 7, wherein the network port comprises a backplane driver, a processor and a network driver.

11. A method of transmitting a message in a programmable logic controller comprising the steps of: providing a router having a router backplane; providing a programmable logic controller connected to the router backplane; providing a plurality of network ports connected to the router backplane; communicating a network message from one of the network ports or the programmable logic controller to the router; and communicating the network message from the router to only an intended destination.

12. The device of claim 1 1, wherein the intended destination comprises a plurality of network ports.

13. The device of claim 11 , wherein the intended destination comprises a plurality of programmable logic controllers.

14. The device of claim 11, wherein the intended destination comprises a single network port.

15. The device of claim 11, wherein the intended destination comprises a single programmable logic controllers.

16. The device of claim 11 , wherein the network port comprises a backplane driver, a processor and a network driver.