System and method for implementing logic control in programmable controllers in distributed control systems

• US 20050085928A1
• Filed: 09/02/2004
• Published: 04/21/2005
• Est. Priority Date: 09/03/2003
• Status: Active Grant

• Current Assignee: Unitronics Limited (Unitronics 1989 R G Limited)
• Original Assignee: Unitronics Limited (Unitronics 1989 R G Limited)
• Inventors: Shani, Haim
• Granted Patent: US 7,225,037 B2
• Time in Patent Office: Days
• US Class Current: 700/18
• CPC Class Codes: G05B 19/056 Programming the PLC

Abstract

The present invention provides a system and method for implementing logic control in programmable controllers in distributed control systems using a wired or wireless network. A software application is used to define the configuration of the network. Based on the network configuration, a compiler engine automatically assigns each statement of the control program to at least one programmable logic controller in the network. Each statement is then transmitted over a data transmission medium to the programmable logic controller assigned to the statement.

Claims

1. A method for implementing a control program in a network of programmable logic controllers having input/output connections, comprising the steps of:

a. translating the control program from a source code into a machine code having a plurality of statements;

b. defining the configuration of the programmable logic controllers and the input/output connections in the network;

c. automatically assigning each statement of the machine code to at least one programmable logic controller based on the defined network configuration; and

d. transmitting each statement over a data transmission medium to the programmable logic controller assigned to the statement.

2. A method as defined in claim 1, further comprising the step of:

a. writing the control program using a plurality of symbolic names to define the input/output connections; and

b. wherein defining the configuration of the programmable logic controllers and the input/output connections in the network includes;

i. linking each symbolic name to at least one input/output connection; and

ii. linking each input/output connection to an address on at least one programmable logic controller.

3. A method as defined in claim 2, wherein linking each symbolic name to at least one input/output connection and linking each input/output connection to an address on at least one programmable logic controller is performed using a textual user interface.

4. A method as defined in claim 2, wherein linking each symbolic name to at least one input/output connection and linking each input/output connection to an address on at least one programmable logic controller is performed using a graphical user interface.

5. A method as defined in claim 1, further comprising the steps of:

a. for each constant and variable set by the statements of the machine code, determining the number of statements which reference the previously set constant or variable; and

b. storing the number of referencing statements and a pointer to each referencing statement.

6. A method as defined in claim 5, further comprising the step of:

a. reassigning at least one of the statements to a different programmable logic controller based on the number of referencing statements.

7. A method as defined in claim 1, further comprising the steps of:

a. identifying at least one external input/output connection referenced by the statements assigned to a first programmable logic controller;

b. identifying a second programmable logic controller having the at least one referenced external input/output connection;

c. adding at least one gluing statement to the control program for notifying the first programmable logic controller of a change at the referenced external input/output connection; and

d. assigning the at least one gluing statement to the second programmable logic controller.

8. A method as defined in claim 7, further comprising the step of:

a. transmitting a message over the data transmission medium from the second programmable logic controller to the first programmable logic controller notifying the first programmable logic controller of a change at the referenced external input/output connection.

9. A method as defined in claim 8, wherein the message is transmitted only if the first programmable logic controller needs to be notified of the change at the referenced external input/output connection.

10. A method as defined in claim 1, further comprising the steps of:

a. identifying at least one external input/output connection referenced by the statements assigned to a first programmable logic controller;

b. identifying a second programmable logic controller having the at least one referenced external input/output connection;

c. adding at least one gluing statement to the control program for instructing the second programmable logic controller to make a change at the referenced external input/output connection; and

d. assigning the at least one gluing statement to the first programmable logic controller.

11. A method as defined in claim 10, further comprising the step of:

a. transmitting a message over the data transmission medium from the first programmable logic controller to the second programmable logic controller instructing the second programmable logic controller to make a change at the referenced external input/output connection.

12. A method as defined in claim 11, wherein the message is transmitted only if the second programmable logic controller needs to be instructed to make the change at the referenced external input/output connection.

13. A method as defined in claim 1, wherein automatically assigning each statement of the machine code to a specific programmable logic controller based on the defined network configuration includes:

a. for each statement, determining the value of more than one binding criteria for each programmable logic controller;

b. for each statement, computing a score for each programmable logic controller, wherein the score is a function of the value of each of the more than one binding criteria and a weight of each of the more than one binding criteria; and

c. assigning each statement to at least one programmable logic controller based on the computed scores.

14. A method as defined in claim 13, wherein the more than one binding criteria is selected from the group consisting of input timing constraints, output timing constraints, CPU usage, memory usage, and communication.

15. A method as defined in claim 1, further comprising the steps of:

a. determining the busyness of each programmable logic controller;

b. reassigning at least one statement from a busy programmable logic controller to a less busy programmable logic controller.

16. A method as defined in claim 15, wherein determining the busyness of each programmable logic controller includes:

a. determining a total CPU usage of the statements assigned to the programmable logic controller;

b. determining a total memory usage of the statements assigned to the programmable logic controller; and

c. computing a busyness index as a function of the total CPU usage and the total memory usage.

17. A method as defined in claim 1, further comprising the steps of:

a. storing the statements in a mirror memory area of each of the programmable logic controllers;

b. instructing each of the programmable logic controllers to stop processing a plurality of old statements stored in a memory area;

c. instructing each of the programmable logic controllers to swap the plurality of old statements stored in the memory area for the statements stored in the mirror memory area; and

d. instructing each of the programmable logic controllers to process the statements.

18. A method as defined in claim 1, wherein the source code is a high-level programming language.

19. A method as defined in claim 18, wherein the high-level programming language is selected from the group consisting of structured text, Basic, C, C++, and Java.

20. A method as defined in claim 1, wherein the source code is a lower-level programming language

21. A method as defined in claim 20, wherein the lower-level programming language is selected from the group consisting of relay ladder logic, state logic, instruction list, ladder diagram, function block diagram, continuous function chart, and sequential function chart.

22. A method as defined in claim 1, wherein the data transmission medium is selected from the group consisting of direct connection, flat cable, plug-in type rack-connection, plug-in type motherboard-connection, fiber-optic cable, twisted-wire pair, and coaxial cable.

23. A method as defined in claim 1, wherein the data transmission medium includes electromagnetic waves.

24. A method as defined in claim 23, wherein the network has a topology selected from the group consisting of star and mesh.

25. A method as defined in claim 23, wherein a radio frequency module and an antenna are embedded in each of the programmable logic controllers.

26. A method as defined in claim 25, wherein the radio frequency module uses a spread spectrum transmission technique.

27. A method as defined in claim 26, wherein the spread spectrum transmission technique is selected from the group consisting of direct sequence and frequency hopping.

28. A method as defined in claim 25, wherein the antenna is selected from the group consisting of printed circuit board antenna and planar inverted-f (type) antenna.

29. A method as defined in claim 25, wherein the network has a mesh topology.

30. A method as defined in claim 29, further comprising the step of:

a. relaying a message from an originating programmable logic controller to a destination programmable logic controller using at least one intermediate programmable logic controller.

31. A method as defined in claim 30, further comprising the step of:

a. tracking in a cost table, in each of the originating programmable logic controllers, the number of intermediate programmable logic controllers between the originating programmable logic controller and the destination programmable logic controller.

32. A method as defined in claim 31, further comprising the steps of:

a. relaying a flood message from the originating programmable logic controller to the destination programmable logic controller using at least one intermediate programmable logic controller;

b. determining the least number of intermediate programmable logic controllers required to relay the flood message;

c. relaying a message comprising the least number of intermediate programmable logic controllers required to relay the flood message, from the destination programmable logic controller to the originating programmable logic controller; and

d. updating the cost table of the originating programmable logic controller.

33. A method as defined in claim 1, wherein transmitting each statement over a data transmission medium to the programmable logic controller assigned to the statement includes relaying at least one statement through a web server.

34. A method as defined in claim 1, further comprising the steps of:

a. establishing a connection between a first web access control client in a first control element and a wide area network;

b. requesting a handle for a second web access control client in a second control element from a web access control server in the wide area network;

c. transmitting the handle from the web access control server to the first web access control client; and

d. transmitting a message from the first control element to the second control element over the data transmission medium wherein the message is not relayed through the web access control server.

35. A method as defined in claim 34, wherein the data transmission medium is selected from the group consisting of direct connection, flat cable, plug-in type rack-connection, plug-in type motherboard-connection, fiber-optic cable, twisted-wire pair, and coaxial cable.

36. A method as defined in claim 34, wherein the data transmission medium includes electromagnetic waves.

37. A method as defined in claim 34, wherein the web access control server is a public server.

38. A method as defined in claim 34, wherein the web access control server is a private server.

39. A system for implementing a control program in a network of programmable logic controllers having input/output connections comprising:

a. a software application for defining the configuration of the programmable logic controllers and the input/output connections in the network;

b. a compiler engine for translating the control program from a source code into a machine code having a plurality of statements and for automatically assigning each statement of the machine code to at least one programmable logic controller based on the defined network configuration; and

c. a host computer for transmitting each statement over a data transmission medium to the programmable logic controller assigned to the statement.

40. A system as defined in claim 39, wherein:

a. the control program is written using a plurality of symbolic names to define the input/output connections; and

b. the software application is configured to link each symbolic name to at least one input/output connection and link each input/output connection to an address on at least one programmable logic controller.

41. A system as defined in claim 40, wherein the software application includes a graphical user interface for linking each symbolic name to at least one input/output connection and linking each input/output connection to an address on at least one programmable logic controller.

42. A system as defined in claim 40, wherein the software application includes a textual user interface for linking each symbolic name to at least one input/output connection and linking each input/output connection to an address on at least one programmable logic controller.

43. A system as defined in claim 40, wherein the compiler engine:

a. for each constant and variable set by the statements of the machine code, determines the number of statements which reference the previously set constant or variable; and

b. stores the number of referencing statements and a pointer to each referencing statement.

44. A system as defined in claim 43, wherein the compiler engine:

a. reassigns at least one of the statements to a different programmable logic controller based on the number of referencing statements.

45. A system as defined in claim 39, wherein the compiler engine:

a. identifies at least one external input/output connection referenced by the statements assigned to a first programmable logic controller;

b. identifies a second programmable logic controller having the at least one referenced external input/output connection;

c. adds at least one gluing statement to the control program for notifying the first programmable logic controller of a change at the referenced external input/output connection; and

d. assigns the at least one gluing statement to the second programmable logic controller.

46. A system as defined in claim 45, wherein the second programmable logic controller is configured to transmit a message over the data transmission medium to the first programmable logic controller notifying the first programmable logic controller of a change at the referenced external input/output connection.

47. A system as defined in claim 46, wherein the second programmable logic controller is configured to transmit the message only if the first programmable logic controller needs to be notified of the change at the referenced external input/output connection.

48. A system as defined in claim 39, wherein the compiler engine:

a. identifies at least one external input/output connection referenced by the statements assigned to a first programmable logic controller;

b. identifies a second programmable logic controller having the at least one referenced external input/output connection;

c. adds at least one gluing statement to the control program for instructing the second programmable logic controller to make a change at the referenced external input/output connection; and

d. assigns the at least one gluing statement to the first programmable logic controller.

49. A system as defined in claim 48, wherein the first programmable logic controller is configured to transmit a message over the data transmission medium to the second programmable logic controller instructing the second programmable logic controller to make a change at the referenced external input/output connection.

50. A system as defined in claim 49, wherein the first programmable logic controller is configured to transmit the message only if the second programmable logic controller needs to be instructed to make the change at the referenced external input/output connection.

51. A system as defined in claim 39, wherein the compiler engine:

a. for each statement, determines the value of more than one binding criteria for each programmable logic controller;

b. for each statement, computes a score for each programmable logic controller, wherein the score is a function of the value of each of the more than one binding criteria and a weight of each of the more than one binding criteria; and

c. assigns each statement to at least one programmable logic controller based on the computed scores.

52. A system as defined in claim 51, wherein the more than one binding criteria is selected from the group consisting of input timing constraints, output timing constraints, CPU usage, memory usage, and communication.

53. A system as defined in claim 39, wherein the compiler engine:

a. determines the busyness of each programmable logic controller;

b. reassigns at least one statement from a busy programmable logic controller to a less busy programmable logic controller.

54. A system as defined in claim 53, wherein the compiler engine determines the busyness of each programmable logic controller by:

a. determining a total CPU usage of the statements assigned to the programmable logic controller;

b. determining a total memory usage of the statements assigned to the programmable logic controller; and

c. computing a busyness index as a function of the total CPU usage and the total memory usage.

55. A system as defined in claim 39, wherein:

a. each of the programmable logic controllers stores the statements in a mirror memory area; and

b. the host computer is configured to instruct each of the programmable logic controllers to stop processing a plurality of old statements stored in a memory area, to swap the plurality of old statements stored in the memory area for the statements stored in the mirror memory area, and to process the statements.

56. A system as defined in claim 39, wherein the source code is a high-level programming language.

57. A system as defined in claim 56, wherein the high-level programming language is selected from the group consisting of structured text, Basic, C, C++, and Java.

58. A system as defined in claim 39, wherein the source code is a lower-level programming language

59. A system as defined in claim 58, wherein the lower-level programming language is selected from the group consisting of relay ladder logic, state logic, instruction list, ladder diagram, function block diagram, continuous function chart, and sequential function chart.

60. A system as defined in claim 39, wherein the data transmission medium is selected from the group consisting of direct connection, flat cable, plug-in type rack-connection, plug-in type motherboard-connection, fiber-optic cable, twisted-wire pair, and coaxial cable.

61. A system as defined in claim 39, wherein the data transmission medium includes electromagnetic waves.

62. A system as defined in claim 61, wherein the network has a topology selected from the group consisting of star and mesh.

63. A system as defined in claim 61, wherein a radio frequency module and an antenna are embedded in each of the programmable logic controllers.

64. A system as defined in claim 63, wherein the radio frequency module uses a spread spectrum transmission technique.

65. A system as defined in claim 64, wherein the spread spectrum transmission technique is selected from the group consisting of direct sequence and frequency hopping.

66. A system as defined in claim 63, wherein the antenna is selected from the group consisting of printed circuit board antenna and planar inverted-f (type) antenna.

67. A system as defined in claim 63, wherein the network has a mesh topology.

68. A system as defined in claim 67, further comprising at least one intermediate programmable logic controller for relaying a message from an originating programmable logic controller to a destination programmable logic controller.

69. A system as defined in claim 68, wherein each of the originating programmable logic controllers is configured to track in a cost table the number of intermediate programmable logic controllers between the originating programmable logic controller and the destination programmable logic controller.

70. A system as defined in claim 69, wherein:

a. the at least one intermediate programmable logic controller is configured to relay a flood message from the originating programmable logic controller to the destination programmable logic controller;

b. the destination programmable logic controller is configured to determine the least number of intermediate programmable logic controllers required to relay the flood message and is configured to transmit a message to the originating programmable logic controller comprising the least number of intermediate programmable logic controllers required to relay the flood message; and

c. the originating programmable logic controller is configured to update the cost table.

71. A system as defined in claim 39, further comprising a web server for relaying at least one statement from the host computer to the programmable logic controller assigned to the statement.

72. A system as defined in claim 39, further comprising a first web access control client in a first control element for:

a. establishing a connection with a wide area network;

b. requesting a handle for a second web access control client in a second control element from a web access control server in the wide area network;

c. receiving the handle from the web access control server; and

d. transmitting a message to the second control element over the transmission medium wherein the message is not relayed through the web access control server.

73. A system as defined in claim 72, wherein the data transmission medium is selected from the group consisting of direct connection, flat cable, plug-in type rack-connection, plug-in type motherboard-connection, fiber-optic cable, twisted-wire pair, and coaxial cable.

74. A system as defined in claim 72, wherein the data transmission medium includes electromagnetic waves.

75. A system as defined in claim 72, wherein the web access control server is a public server.

76. A system as defined in claim 72, wherein the web access control server is a private server.