PLC executive with integrated web server

• US 6,640,140 B1
• Filed: 10/10/2000
• Issued: 10/28/2003
• Est. Priority Date: 10/10/2000
• Status: Expired due to Term

• Current Assignee: Schneider Automation Incorporated (Schneider Electric SE)
• Original Assignee: Schneider Automation Incorporated (Schneider Electric SE)
• Inventors: Harriman, Merrill W., Lindner, David T., McGlaughlin, James W. III, Swales, Andrew G.
• Primary Examiner(s): PATEL, RAMESH B
• Application Number:
  US09/685,355
• Time in Patent Office: 1,113 Days
• Field of Search: 700/9-13, 700/18, 700/19, 700/20, 700/23, 700/65, 700/66, 700/83, 700/86, 700/87, 709/106, 709/107, 709/220, 709/221, 709/223, 709/224, 709/225
• US Class Current: 700/18
• CPC Class Codes: G05B 19/0421 Multiprocessor system
• CPC Class Codes: G05B 19/052 Linking several PLC's
• CPC Class Codes: G05B 2219/1214 Real-time communication between plc, Ethernet for configuration, monitor
• CPC Class Codes: G05B 2219/1216 Interlock problem, avoid sending data to slave when slave processes data
• CPC Class Codes: G05B 2219/15081 Period length ratio between application and communication task is settable
• CPC Class Codes: G05B 2219/23217 Parallel processing
• CPC Class Codes: G05B 2219/31186 TCP-IP internet protocol
• CPC Class Codes: G05B 2219/34038 Web, http, ftp, internet, intranet server

Abstract

A programmable logic controller for use as part of an industrial control system or as part of an automated system and a corresponding method, the controller including an interface to the Internet, and including a web server allowing a remote computer to access web pages maintained by the controller providing information relevant to the control function of the controller such as control sensor readings and, optionally, information about the status of the control system. The web server is implemented as part of the controller in such a way that the controller scan rate (the rate at which the ladder logic for all associated control system devices is repeated) is unaffected by execution of the web server.

Claims

1. A controller for use as part of an industrial control system or as part of an automated system, the controller for controlling at least one input/output device, the controller capable of interacting with a remotely located computer via a network, the controller comprising:

a) means for executing a controller scan including solving ladder logic associated with the at least one controlled input/output device, the controller scan having a predetermined scan rate;

b) a web server for gathering data relevant to a control function, the web server being responsive to a request for the data from the remotely located computer; and

c) web pages comprising data and associated instructions retrievable and executable by the remotely located computer, the instructions causing the remotely located computer to present the data for display in a predetermined format;

wherein in response to a request for data, the web server provides one or more web pages in which the requested data are displayed, and further wherein the web server and the means for executing a controller scan are hosted by a same programmable logic controller device.

2. The controller of claim 1 wherein the web server executes as a background task.

3. The controller of claim 1 wherein the web server executes in parallel with the means for executing the controller scan.

4. The controller of claim 1 wherein in response to a request for data from the remote computer, the web server provides no more than a predetermined maximum number of bytes of combined data and instructions per scan by the means for executing the controller scan.

5. The controller of claim 4, wherein the maximum number of bytes per scan is predetermined to be a number of bytes that can be communicated to the network for delivery to the remote computer in less than the time required for one scan by the means for executing the controller scan.

6. The controller of claim 1, wherein at least some of the data are resident on a different controller, the data-gathering means being configured to access and obtain the data from the different controller via a computer network.

7. The controller of claim 1, wherein the controller further comprises a transmission control program (TCP)/Internet protocol (IP) stack customized to communicate any MODBUS command or message as a single TCP/IP packet.

8. The controller of claim 7, wherein the web server comprises a file server for providing the web pages.

9. The controller of claim 8, wherein the web server further comprises a hypertext transfer protocol (HTTP) server providing file get functionality.

10. The controller of claim 9, wherein the web server further comprises a file transfer protocol (FTP) server for receiving new or replacement web pages over the network via the TCP/IP stack and provides them to the file server.

11. The controller of claim 7, wherein the means for executing the controller scan is coupled to a MODBUS handler, which in turn is interfaced to the TCP/IP stack, thereby coupling the means for executing a controller scan to the network.

12. The controller of claim 7, wherein the means for executing the controller scan is coupled to a local network input/output interface thereby coupling the means for executing the controller scan to a local network.

13. The controller of claim 1, further wherein the web server checks for a request for the data, and if a request is present, then the web server services the request, but does not service the request for more than a predetermined length of message, the predetermined length of message such that the web server is able to service a message of the predetermined length in less time than is required for a single controller scan, thereby maintaining the predetermined scan rate as the rate of scanning.

14. A method of controlling at least one input/output device of an industrial control system or automated system and of interacting with a remotely located computer via a network, the method comprising the steps of:

a) executing a controller scan including solving ladder logic associated with the at least one controlled input/output device, the controller scan having a predetermined scan rate;

b) gathering data relevant to a control function;

c) storing web pages comprising data and associated instructions retrievable and executable by the remotely located computer, the instructions causing the remotely located computer to present the data for display in a predetermined format;

d) checking for a request for the data; and

e) if a request for the data is present, then responding to a request for the data from the remotely located computer by providing one or more of the web pages used to display the requested data;

wherein all of the steps are performed according to instructions hosted by a same programmable logic controller device.

15. The method of claim 14, wherein the step of gathering data and the step of responding to a request for the data are executed as background tasks.

16. The method of claim 14, wherein the step of gathering data and the step of responding to a request for the data execute in parallel with the step of executing the controller scan.

17. The method of claim 14, wherein in responding to a request for data from the remote computer, no more than a predetermined maximum number of bytes of combined data and instructions per scan are provided.

18. The method of claim 17, wherein the maximum number of bytes per scan is predetermined to be a number of bytes that can be communicated to the network for delivery to the remote computer in less than the time required for one scan.

19. The method of claim 14, further comprising the step of communicating over the network MODBUS commands or messages, wherein any MODBUS command or message is communicated over the network as a single TCP/IP packet.

20. The method of claim 14, wherein in responding to a request for the data, the request is serviced, but it is not serviced for more than a predetermined length of message, the predetermined length of message such that the a message of the predetermined length is able to be serviced in less time than is required for a single controller scan, thereby maintaining the predetermined scan rate as the rate of scanning.