Network Programmable Logic Controller System

1. Field of the Invention

The invention relates to the field of programmable logic controllers which are used to control machinery and equipment for automated and partially automated assembly lines. The controllers are programmed by the use of ladder diagrams wherein elements of a ladder diagram represent relays, switches and the like associated with the equipment and machinery on the assembly line.

2. Prior Art

Prior art programmable logic controllers can be directly coupled to up to 16 peripheral controllers which serve to interface the assembly line machinery and equipment to the programmable logic controller. Additionally, prior art programmable logic controllers can indirectly control six additional racks of sixteen peripheral controllers by using local rack adapters, there being one local rack adapter for each rack of sixteen peripheral controllers, for a total of 896 inputs and 896 outputs (assuming 8 inputs and 8 outputs per peripheral controller). Ladder diagrams which are, in effect, the program used by the programmable logic controller to generate the appropriate control, data and address signals for the peripheral controllers, are created and edited using a separate processor such as a personal computer or minicomputer. The completed ladder diagram is recorded on magnetic tape or disk which is removed from the processor which created the ladder diagram, and read into the memory of the programmable logic controller through a disk or tape drive connected to the programmable logic controller. A representative prior art programmable logic controller is a Model 700 Controller manufactured by Square D Company.

Prior art ladder editors are typically part of the programming panel of the prior art programmable controllers.

The present invention is directed to a programmable logic controller system having the capability of controlling up to 64 clusters of peripheral controllers, wherein each cluster has up to seven racks of peripheral controllers, each rack having up to 16 individual peripheral controllers. Excepting for the cluster containing the programmable logic controller, each cluster is coupled to the programmable logic controller through an ethernet cable to a cluster controller. Each of the seven racks of peripheral controller cards is connected to its respective programmable logic controller or cluster controller directly (for the first rack) or through a local rack adaptor (for the other six racks). The programmable logic controller generates data, address and control signals which are used by the peripheral controllers to operate machines and equipment on an assembly line. The data, address and control signals are generated by a ladder diagram created and modified in a separate personal computer, which may be coupled to the programmable logic controller through an ethernet cable. The code representing the ladder diagram created in the personal computer is downloaded through the ethernet cable to the programmable logic controller. The ladder diagram is created and edited using a ladder editor program having the following features: scrolling, zoom in/out, free format line drawing, real time incremented compiler/linker, dynamic reconfiguration.

Assuming an eight bit data path, each peripheral controller controls up to eight points such as an on/off switch. Since each controller has an input channel and an output channel, there are, in effect, 16 control lines available per controller, although only 8 are available at a time for input or output Thus, within a group of 16 peripheral controllers, up to 256 points may be controlled (128 input points and 128 output points). Within a cluster of 7 racks of 16 peripheral controllers, up to 1792 points can be controlled with a single programmable logic controller (and 6 local rack adaptors). Similarly, when the full complement of 64 clusters is installed, up to 114,688 points can be controlled by the single programmable logic controller, 63 cluster controllers and 384 local rack adaptors (i.e., six local rack adaptors per cluster).

Additionally, using a personal computer coupled to the programmable logic controller through an ethernet cable, the ladder diagram used in the system can be easily and dynamically modified as required.

FIG. 1 is an overview diagram of the invented programmable logic controller system showing the use of a single programmable logic controller to control up to 64 clusters, each containing seven racks of peripheral controllers.

FIG. 2 is an overview block diagram showing the various functional elements coupled to a programmable logic controller for use in the present invention.

FIG. 3 is a block diagram showing the components of a programmable logic controller for use in the invented system.

FIG. 4 is an overview block diagram illustrating the relationship of various software tasks necessary to implement the invented programmable logic controller system.

Referring first to FIG. 1, the components of the invented programmable logic controller system are shown as personal computer (PC) 11 which is coupled through an ethernet cable 13 to programmable logic controller (PLC) 15. PLC 15 controls up to sixteen peripheral controllers 17 directly and, indirectly, six additional local racks, each having up to sixteen peripheral controllers, through local rack adaptors 21. PLC 15 is also shown coupled through an ethernet cable to up to 63 cluster controllers 25. In this manner, PLC 15 and each cluster controller 25, directly control up to sixteen peripheral controllers 17, and indirectly control up to sixteen peripheral controllers in each of six racks through six local rack adapters 21. Within a cluster, each local rack adapter is coupled to its adjacent local rack adapter, cluster controller or PLC by a 50 conductor cable.

FIG. 2 illustrates in further detail the relationships between the major components of the invented programmable logic controller system. Specifically, PLC 15 is coupled to peripheral controller 17 through an 8 bit data bus 27, a six line control bus 29 and an 8 bit address bus 31.

PLC 15 is coupled to PC 11 through an ethernet cable 13. Personal computer 11 may be any commercially available personal computer, but in the preferred embodiment, is an IBM PC/XT, IBM PC/AT or compatible. PC 11 performs three tasks which are shown in FIG. 2 as the compiler task 35, the editor task 37 and the communications task 39. The compiler task should have the capability of generating executable object code from ladder diagram source code on a line by line basis. A suitable compiler task which may be used in the present invention is disclosed in U.S. Pat. No. 4,722,071 which issued Jan. 26, 1988. Editor task 37 and communications task 39 will be described in detail below.

PLC 15 in the present invention performs the three tasks which are shown in FIG. 2 as the basic input output system (BIOS) task 45, communications task 47 and ladder logic control task 49. Ladder logic control task 49 includes linker sub task 51 and parallel logic and I/O control sub task 53. Details of each of the foregoing tasks and sub tasks will be described below. The logical relationships between the foregoing tasks and subtasks is shown in FIG. 4, which shows the PC 11 tasks under control of a PC multitasking executive shell and the PLC 15 tasks and subtasks under control of a PLC multitasking executive shell.

The components necessary to implement PLC 15 in the present invention are shown in block diagram form in FIG. 3 and comprise input/output scanner 55 and logic scanner 57.

Input/output scanner 55 includes a central processing unit (CPU) 61, random access memory (RAM) 63, read only memory (ROM) 65, ethernet ports 67 and 69 and parallel I/O ports 71 and 73.

Logic scanner 57 comprises PAL control logic 81, bit sliced processor 83, program RAM 85 and data RAM 87.

Editor task 35 creates and modifies ladder source code. As each rung of the ladder is created or modified, a pointer to that rung is sent to compiler task 37. When the task is initiated, an initialization step takes place which loads into memory a selected ladder diagram or a default ladder diagram. Once the initialization has been completed, an edit step commences which sets up a screen display of the ladder in memory and then executes a program loop which performs one of three types of editing as follows: (a) normal mode; (b) line mode; or (c) data monitor mode. Normal mode has two sub-modes namely element mode and command mode. In element mode, the various elements of the ladder are entered. In command mode, editing and supervisory commands are entered. In line mode, elements entered in normal mode are connected. In data monitor mode, blocks of ladder data are displayed in various formats.

Compiler task 37 creates object code for each rung from the source code created or modified by editor task 35. Additionally, compiler task 37 may compress the source code by removing unused fields in the source. A complete description and source code listing for a suitable compiler task 37 is set forth in U.S. Pat. No. 4,722,071 which issued Jan. 26, 1988.

Communications task 39 formats object code and compressed source code generated by compiler task 39 into ethernet packets which are transmitted over ethernet cable 13 to communications task 47 in PLC 15.

BIOS task 45, which is a multitasking executive, is the basic input/output operating system for PLC 15.

Communications task 47 obtains ladder diagram object code and compressed source code for each rung by decoding ethernet packets sent by communications task 39. Once all necessary packets have been received and assembled, communications task 47 invokes linker sub task 51 of ladder logic control task 49.

Ladder logic control task 49 downloads and uploads ladder object code and source code. Linking of downloaded ladder object code and execution of the linked code are performed by linker subtask 51 and parallel logic and I/O control subtask 53.

Linker subtask 51 takes rungs generated compiler task 37 and adds to or replaces rungs in the ladder stored in program RAM 85.

Parallel logic and I/O control subtask 53 performs the interrelated functions of I/O scan and logic scan. In particular, during an I/O scan, a program in ROM 65 causes CPU 61 to write data from RAM 63 to peripheral controllers 17, and read data from the peripheral controllers for storage in RAM 63. During a logic scan, based upon a program in RAM 85 (the object code representing a ladder diagram), new output values to be sent to the peripheral controllers during an I/O scan are calculated based upon current input values stored in RAM 63.

CPU 61 is a Motorola 68010 or equivalent. RAM 63 is 128K by 16 bit RAM available from a number of sources. ROM 65 is a 32k by 16 bit EPROM. ROM 65 stores BIOS task 45. Ethernet ports 67 and 69 are AMD part numbers 7990 or equivalent and required support circuity. Ethernet port 67 handles the receipt and transmission of ethernet packets between communications task 39 and communications task 47. Ethernet port 69 handles the receipt and transmission of ethernet packets between communications tasks in cluster controllers 25.

Parallel I/O ports 71 and 73 are standard parallel I/O ports which may be implemented in a variety of ways, the particulars of which are well know to persons skilled in the art. The details regarding a data bus, address bus and control bus, as well as timing and power considerations necessary for the proper operations of such components are well known to those skilled in the art and will be described herein only to the extent necessary for a proper understanding of the invention.

Cluster controllers 25 are similar to input/output scanner scanner 55, but do not have ethernet port 67 or logic scanner 57.

PAL control logic 81 is a set of eight PALs (programmable logic array) which contain the logic equations or microcode used to control the operation of bit sliced processor 83. In the preferred embodiment, the logic in the eight PALs perform the functions (i) logic scanner condition test logic; (ii) logic scanner program counter 1 (external load); (iii) logic scanner program counter 2; (iv) logic scanner program counter 3; (v) logic scanner sequencer and interface logic; (vi) logic scanner control store bus interface logic; (vii) logic scanner internal bus control logic; and (viii) logic scanner control store parity logic. The particulars of the PALs and their logic equations which perform these functions are set forth in appendix 1.

Bit sliced processor 83 is a 16 bit microprocessor available as from Advanced Micro Devices as its part number Am29116.

Program RAM 85 is a 32K by 64 bit RAM which contains executable ladder object code generated by compiler task 37 and linked by linker task 51.

Data RAM 87 is a 32K by 16 bit RAM which stores the status of each data point controlled by the system. In a fully configured system (i.e. 64 clusters of 7 racks, 16 peripheral controllers per rack for a total of 114,688 points), only 7K of storage is required. This 7K portion of RAM 87 is bit mapped to corresponding data points. The remaining 25K portion of data RAM 87 is available for use as temporary storage by the executing ladder diagram.