Industrial Automation course

Transcription

1 Industrial Automation course Lesson 5 PLC - SFC Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 1

2 History Before the 60s the SEQUENTIAL CONTROL was seen as EXTENSION OF THE CONTINUOUS CONTROL or in the best cases THE DIGITAL. Since the '60s the theory on finite state automata is developed, whose formal models allow a deep MATHEMATICAL ANALYSIS, but hardly useful for DESIGN of the algorithms. In the 70's the design of automation systems is quite elementary, is based on CIRCUITAL REPRESENTATIONS or TEXTUAL DESCRIPTIONS. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 2

3 History In the 1975, in France, a commission for the FORMALIZATION of a DESCRIPTIVE PROJECTUAL instrument oriented to the SEQUENTIAL CONTROL is instituted. GRAFCET is born. In the 80s GRAFCET is defined as SEQUENTIAL FUNCTIONAL CHART in the IEC (International Electrotechnical Commission) 848. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 3

4 Base elements State (phase) Definition The STATE is a defined OPERATIVE CONDITION of a part of the complex system. Graphical representation Initial state with the double border N N State number or better a univocal Name Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 4

5 Base elements State (phase) Remarks The STATE is an INVARIANT condition of the system under exam, it can change or being modified only as a result of an EVENT. During the dynamic evolution of the complex system, each STATE of each part of the system can be only in two possible conditions: ACTIVE or INACTIVE. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 5

6 Base elements State (phase) Syntax The PLC defines, for each state, two variables: MARKER, the Boolean variable that contain the condition of the state (it sais if it is active or not) TIMER, the internal variable that represents the elapsed time since the activation (if the state is active) Usually MARKER variable: StateName.X TIMER variable: StateName.T Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 6

7 Base elements Action Definition All the OPERATIONS executed from the system under exam, when it is in a defined OPERATIVE CONDITION (STATE), are called ACTIONS. Graphical representation N Action 1 Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 7

8 Base elements Action Remarks Each STATE of the system in made of a defined set of ACTIONS. From the CONTROL SYSTEM field of view, considering that it is used for the execution of the LOGIC-SEQUENTIAL SOFTWARE, an ACTION corresponds to one or more PROCEDURES, that are a SET of INSTRUCTIONS, executed in series, until the STATE is ACTIVE (until an EVENT changes the STATE). Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 8

9 Base elements Action Syntax The PLC defines, for each action, three variables: A m, the univocal id of the action Q m, that defines the action type (qualificator) V m, a Boolean variable that represents the state of the action N.B.: In a lot of programming environments, the actions (and also the transitions) can be defined with one of the IEC programming languages Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 9

10 Base elements Action Syntax Qualificator types N: Normal non stored If the action A n is of type N it will be executed each PLC cycle if the state connected to it is active P: Pulse If the action A n is of type P it will be executed only the first PLC cycle in which the state connected to it is active N.B.: Sometimes it is possible to find the qualificator I (Impulise) Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 10

11 Base elements Azione Syntax Qualificator types S: Set If the action A n is of type S it will be executed each PLC cycle until the same A n action (in a subsequent state) will have the R qualificator R: Reset If the action A n is of type R (as already described) stops the execution of a previous action enabled with a S qualificator Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 11

12 Base elements Azione Syntax Qualificator types L: Limited Time If the action A n is of type L it will be each PLC cycle for t#ts seconds, starting from the state activation N.B.: if the state is disabled, the action is terminated D: Time Delayed If the action A n is of type D it will be executed each PLC cycle after t#ts seconds from the state activation Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 12

13 Base elements Azione Syntax Qualificator types SD: Stored / time Delayed If the action A n is of type SD it is equal to a S action, with a delay of t#ts seconds SL: Stored / time Limited If the action A n is of type SL it is equal to a S action, disabled after t#ts seconds (independently from the active state) Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 13

14 Base elements Transition Definition(s) The PASSAGE from a PREVIOUS STATE to a SUBSEQUENT one, because of an event, is called TRANSITION. The LOGICAL check, that determines the happening of an EVENT is called CONDITION. Remarks Each CONDITION is associated to a TRANSITION. Each CONDITION is defined as a LOGICAL FUNCTION, through a BOOLEAN EXPRESSION that can be TRUE or FALSE. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 14

15 Base elements Transition Graphical representation N Action 1 Transition Condition N+1 Action 2 Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 15

16 Evolution rules Very important Rule 1 A transition is defined as ENABLED if ALL the phases above of it are active. A transition is defined as SUPERABLE if it is enabled and the condition related to it has the value «true». Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 16

17 Evolution rules Rule 2 When a transition is superable it is overcome: all the phases above the transition are disabled, while those below it are enabled It is very easy: when the condition becomes true all the below phases are enabled and the above are disabled N.B.: the correct syntax is always state - transition - state - transition - Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 17

18 Evolution rules Example 1 2 True False 3 Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 18

19 Base structures Defined the previously defined rules, the base structures that can be created are the following: If then else 1 Choice A B 2 3 C D Convergence 4 Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 19

20 Base structures Remarks The A and B conditions must be mutually exclusive. If they were not it would risk having the phase 4 activated «two times». A C 4 B D N.B.: As it will be showed in the last part of the course, this is a difference between the SFC and the Petri nets. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 20

21 Base structures Parallel 1 Parallelism A 2 3 B Synchronization 4 Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 21

22 Base structures Remarks The phases 2 and 3 are activated simultaneously. In the case of presence, in one of the branches, of more than one phase, the Check of the condition B is executed when the Last phase of each branch is activated A B Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 22

23 SFC in a real case In a lot of development environments (also in the case of the B&R Automation Studio) the SFC is integrated with the other IEC languages. It means tat, in each phase (called «state»), it is possible to associate the execution of a portion of code written in one of the 1131 languages. For this reason, not all the action types described before are used inside the tool. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 23

24 Example Base example state1 What happens if A and B are both true? The PLC continues to commutate cyclically between the state 1 and the 2 A state2 B Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 24

25 Example Action and if then else example Develop a software that allow, using the activation of an actuator for 1 second, to discard products with a weight lower to a defined threshold Inputs PC: Photocell Weight: weight of the product Outputs Actuator: activation of the actuator Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 25

26 Example N.B.: With Automation Studio, if we want to use the IEC norm, in order to create actions, it is necessary to click on the button «Use IEC Steps» as depicted in the picture. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 26

27 Example Action and if then else example Waiting R Actuator PC Product Arrived Weight>=Threshold Weight<Threshold Discard S Actuator Discard.T>=t#1s Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 27

28 Example Temporally limited states example Develop a software that activates the electro-valve U if the overfull sensor OFS remains active for more than 10 s and keeps it activated for 30 s Inputs OFS: Overfull sensor Outputs U: Electro-valve activation Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 28

29 Example Temporally limited states example Sensor Check Sensor Active OFS NOT(OFS) Valve Active SensorActive.t>=t#10s N U ValveActive.T>t#30s Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 29

30 Example Other languages actions example Develop a software that advise for the passage of the tenth customer, using a photocell on the entrance of the shop Inputs PC: photocell N.B.: usually, during the exercises, where it is required to implement a SFC software, if not specified, this type of solution is denied Outputs Tenth: reach of the tenth customer Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 30

31 Example Other languages actions example Customer Wait PC Customer Arrived N<10 Tenth Reached N>=10 FALSE Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 31

32 Example Other languages actions example Customer Wait PC Customer Arrived E PC := FALSE; N := N + 1; N<10 Tenth Reached N>=10 FALSE We can add actions on the Entrance (E), Cyclically (C) and on the exit (X), in this case we use the structured text Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 32

33 Example Other languages actions example Customer Wait PC Customer Arrived N<10 Tenth Reached N>=10 FALSE E Tenth := TRUE; Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 33

34 From SFC to Ladder It is possible to translate a software implemented in SFC, in a Ladder software, using simple rules, independent from the program itself. In the course we will focus on the algorithm without stability search. N.B.: These are standard rules, applicable to every SFC program! Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 34

35 From SFC to Ladder Consider this SFC evolution algorithm This algorithm is called without stability search. Input reading Phases initialization In the case of non-stable phase (phase with, on the activation, the exiting transition set to true), this scheme «makes a mistake»: If the action is continuous must not be activated If it is impulsive, it must be Impulsive actions execution Inputs reading Definition of the superable transitions Definition of the new condition Outputs update Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 35

36 From SFC to Ladder Just for information, this is the algorithm with stability search Inputs reading Phases initialization Impulsive actions execution Inputs reading Definition of the superable transitions Definition of the new condition Impulsive actions execution Conditions isn t changed Outputs update N.B.: we will use the other one Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 36

37 From SFC to Ladder The Ladder must be defined with four sections: Initialization Executed only during the first step of the software Actions execution Enabling of the actions connected to the active phase Transitions evaluation Enabling of all the active transitions Conditions update Check of the passage between the active phases and the following Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 37

38 From SFC to Ladder Initialization FP True True Cyclic LBL Cyclic JMP L U N.B.: in AS, this part can be directly implemented in the _INIT! Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 38

39 From SFC to Ladder Actions execution For each continuous action a rung is used, connected in OR, with all the other that activate the same action PhaseA PhaseB ActionA ActionB For the stored activities it is possible to use SET RESET coils ActionC For the impulsive actions it is possible to create the network for the generation of the impulse Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 39

40 From SFC to Ladder Conditions evaluation For each phase, the outgoing conditions that enable the transition are verified In the case of parallel transitions it is necessary to use the AND structure with the Boolean signals of the phases PhaseA CondA PhaseB PhaseCCondD TransA TransB TransB Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 40

41 From SFC to Ladder Condition update When a transition is active, all the above phases are disabled, while the below are enabled TransA PhaseA U PhaseB L TransB PhaseC U PhaseD Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 41 L