PLC Programming Manual Introduction - …

1 PLC Programming Manual Page 1 PLC Programming Manual Introduction This Manual is intended for machine builders, technicians, dealers, and others who need to look under the hood of the PLC system. The PLC (Programmable Logic Controller) is the portion of the control system, which deals with accessory equipment; that is, anything installed on the machine beyond the servo motors themselves. Spindle control, coolant control, limit switches, fault signals, pushbuttons, indicator lights, etc. are all controlled through the PLC.

2 The PLC system has two possible configurations. The first configuration consists of a hardware I/O board which provides the electrical interface to all the switches and relays (RTK3, PLCIO2, RTH2, PLC15/15, ect.), the jog panel with its keys and LEDs, and a software logic program which is executed on the CPU10 controller board ( Program). In the first configuration (see figure 1) the PLC program, which is executed on the CPU10, is contained in the file The control software sends to the CPU10 on startup.

3 Once running on the CPU10, the logic program receives inputs from the PLC I/O board, from the jog panel, and from CNC programs. It sends outputs back to all three places: for example, turning on output relays on the I/O board; turning on LEDs on the jog panel; and sending signals such as Feed Hold to the CNC processor. Figure1: PLC I/O Configuration 1 The first PLC configuration, using the program only, is limited in size and functionality and cannot control complex machine hardware such as a tool changer, which may require timers, counters, ect.

4 For machines that need more PLC program functionality a second PLC configuration is used. The second configuration consists of all elements of the first configuration plus a second PLC program ( ) running in the servo PC memory. program running on CPU10 CNC10 control software running G code programs Jog Panel PLC Servo PC Memory CPU10 PLC Programming Manual Page 2 program is still running on the CPU10 and is used in conjunction with the The reason we need two PLC programs running is the new program doesn t have access to all of the I/O so the program needs to be there to control those I/O bits.

5 A minimal program can be made by echoing memory bits to the outputs you need to control. Then you can control those memory bits in the program thus making it possible to control virtually everything needed in the PC PLC program. Figure 2: PLC I/O Configuration 2 While the PLC program has access to many features of the jog panel, it has no access to the jogging controls themselves. The axis jog buttons, Fast/Slow and Inc/Cont buttons, the jog increment buttons, and the MPG handwheel are all directly handled by code on the CPU7.

6 The first section of the PLC Manual will explain Programming for the program, then move into more complex issues and the or extended PLC Programming . Language The PLC Programming language is a simple statement-based logic language. At first it may seem far removed from the ladder logic diagrams familiar from other PLC systems. program running in servo PC memory. CNC10 control software running G code programs Jog Panel PLC program running on CPU10 CPU10 Servo PC Memory PLC Programming Manual Page 3 However, each assignment statement in a PLC program is equivalent to one rung of a PLC ladder.

7 One or more inputs are logically combined to produce one output. The PLC supports four logical operators: AND, OR, XOR, and NOT. They may be abbreviated using the symbols & (AND), | (OR), and / (NOT). There is no abbreviation for XOR. Parentheses may be used for logical grouping. In the absence of parentheses, the operators follow normal mathematical precedence: NOT, AND, XOR, OR. The = sign is used to store a logical result (an input of combination of inputs) in an output location. These operators are used to manipulate 240 data bits: 80 inputs, 80 outputs, and 80 memory locations.

8 Many of the inputs and outputs are permanently mapped to particular hardware devices. The memory locations are not mapped to any hardware, but some are reserved for special purposes. The data bits are given default names such as INP1, INP2, INP80, OUT1, OUT41, MEM27, Typically the first part of a PLC program file assigns alternate names to these default tokens. For example, the line Emergency_stop IS INP11 tells the PLC program compiler that the name Emergency_stop is equivalent to INP11. You can then use the more intuitive name for the remainder of the program.

9 It is important to distinguish between IS , which assigns alternate names, and = , which actually stores computed bit values. A line using IS doesn t actually do anything in the PLC program; it simply provides information to the compiler about the names you will be using. A line using = has a real effect each time the program runs. Let us look at a simple latched input structure: suppose that we have a relay connected to OUT1 which controls a work light. We want the Aux1 key on the jog panel to turn the light on, and the Aux2 key to turn it off.

10 In the definitions sections of the program we would have: Aux_1_key IS INP49 Aux_2_key IS INP50 and Work_light IS OUT1 In the statement section which follows we would have Work_light = ( Work_light OR Aux_1_key ) AND / Aux_2_key PLC Programming Manual Page 4 This statement says that the relay will be on if it was already on or if the Aux1 key is pressed, as long as the Aux2 key is not pressed. In traditional ladder logic this would appear as follows: The PLC compiler is not case sensitive. However, it is a good idea to write your PLC programs using consistent capitalization.