Unlike an organizational chart, which allows a general description of an automation well suited to programming, but which is nevertheless poor in a sequential domain and does not highlight the simultaneous operations, the Grafcet is a graphic model representing the functional specifications of a logic automation, which describes all the behaviors of the control automation in the face of events arising from the process by imposing a rigorous approach, possibly hierarchical, thus avoiding inconsistencies, blockages or conflicts in operation. The drawing shows in Figure 1 an example of Grafcet associated with the automation cycle of a powder compression press, this example of Grafcet is taken from the draft standard NF of October 27, established by the Technical Union electricity. In this FIG. Such a press essentially comprises a fixed lower punch 3 , an upper punch 1 and a movable die 2 , as well as a system for evacuating the compressed part not shown in the drawing.
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Unlike an organizational chart, which allows a general description of an automation well suited to programming, but which is nevertheless poor in a sequential domain and does not highlight the simultaneous operations, the Grafcet is a graphic model representing the functional specifications of a logic automation, which describes all the behaviors of the control automation in the face of events arising from the process by imposing a rigorous approach, possibly hierarchical, thus avoiding inconsistencies, blockages or conflicts in operation.
The drawing shows in Figure 1 an example of Grafcet associated with the automation cycle of a powder compression press, this example of Grafcet is taken from the draft standard NF of October 27, established by the Technical Union electricity.
In this FIG. Such a press essentially comprises a fixed lower punch 3 , an upper punch 1 and a movable die 2 , as well as a system for evacuating the compressed part not shown in the drawing. The working cycle of such a press is as follows The matrix 2 and the upper punch 1 being in the high position, the material is introduced into the lower punch 3. Once the material in place, the upper punch 1 descends, compresses the material by entering the matrix then rises in the high position.
The matrix 2 then descends on the lower punch in order to release the part 4 which has just been compressed and this is then evacuated. The Crafcet corresponding to this cycle is shown schematically on the left in Figure I; it includes six steps - Step 1: placement of the material - Step 2: lowering the punch - Step 3: raising the punch - Step 4: lowering the matrix - Step 5: evacuation of the compressed part - Step 6: ascent of the matrix. Each transition is associated with certain conditions, constituting the "receptivity" of the transition.
The next step can only be triggered if the conditions of the associated transition are fulfilled, that is to say only if its receptivity is true. In this example, the receptivity of the transitions between each step will be as follows - Transition Tl2 : material in place and cycle start - Transition T23 : end of compression - Transition T34 : punch at the top - Transition T45 : matrix at the bottom - Transition T56 : evacuated room - Transition T61 : matrix at the top.
Thus, for example, step 2 can only be triggered if the material is in place and if the start of the cycle has been triggered, these two conditions constituting the receptivity of the transition A step can be active or inactive. When the step is active, the action associated with it must be performed, so for example when step 3 is active, the upper punch 1 must go up. The essential purpose of a Grafcet is to define in a clear and unambiguous way the functional specifications which an automatic control must meet.
However, the realization of an order program from a Grafcet becomes delicate and risky as soon as the process to be automated becomes too complicated and important. The aim of the present invention is therefore to provide a method making it possible to pass directly from the Grafcet of a process to the control thereof, so as to avoid any human intervention between the graphic representation of the latter and its technological materialization. This object is achieved using the method according to the invention which corresponds to - freeze the information or entries emanating from the process to be automated, the freezing of each information or entry being carried out only when this information is used during the cycle - determine from this information and according to the planned control law, the actual evolution of the Grafcet of the system; - communicate the new established guidelines to the process.
The freezing of information inputs is therefore not a specific operation in itself, but is integrated into the process of determining the conditions of evolution receptivity. The acquisition of an input quantity is only carried out during a receptivity calculation where this quantity intervenes.
However, in order to ensure the uniqueness of the acquisition, an appropriate marking is put in place. This part of the process therefore consists in breaking up the functional operation of freezing the inputs over the entire duration of a cycle. This phase makes it possible to memorize the state of the operative part for the entire duration of the cycle and therefore to guard against possible developmental contingencies which could be generated by a change, during the cycle, of one or more quantities s of entry.
The evolution of Grafcet leads to provoking changes of states of the output quantities, quantities which can themselves serve as inputs for other parts of the control law. In order not to cause a change in the input values, as long as the control law is evolving, the modifications of the output quantities, which serve as new input quantities or setpoints, are therefore only carried out.
Advantageously, in this process, the evolution of the Grafcet of system is performed cycle after cycle, a cycle corresponding to the fran change of all the transitions that can be crossed at a given time.
This method thus makes it possible to evaluate all the cases presented and to determine undermine the next system situation. Advantageously also, the phase of updating the outputs, which become the new inputs for the next cycle, is limited to updating only the outputs that have evolved during the cycle, which makes it possible to reduce the amount of gold in this phase.
To predict the evolution of Grafcet, it was necessary to find a simulation process that could be implemented without requiring too long processing times or the implementation of too many indicators. Indeed, a Grafcet simulation process which immediately comes to mind consists in determining the evolution of Grafcet from all the existing stages. However, such a method is not at all optimized, in particular when it comes to treating important Grafcet, because it involves the examination of situations which cannot evolve and therefore an excessive loss of time.
A second method consists in being interested in the examination of the active stages in order to determine the activatable or deactivable stages of the system. However, the implementation of such a method is very cumbersome and complex and requires too many indicators.
The method of simulating the evolution of Grafcet according to the invention makes it possible to avoid these drawbacks, since it is based on the study of validated transitions. Indeed, the examination of the validated transitions also gives indications on the active or non-active stages because a transition is only validated when the immediately preceding stages are active. This process consists of: - A determine which of the validated transitions will become 1? At the end of this process, the activated and deactivated steps of the cycle examined are therefore obtained, which makes it possible to determine the new output states of the system and to update the state of the outputs.
Advantageously, the determination among the validated transitions of those which become passable is carried out by calculating the receptivity associated with each validated transition from the input values read at the start of each cycle, a validated transition becoming passable when its receptivity is true.
The calculation of the receptivities associated with each transition that can be crossed in step A also makes it possible to determine the transitions which are likely to remain validated during the next evolution cycle, these transitions having a false receptivity. These transitions likely to remain validated are classified in a particular set of transitions to be re-examined in step A and will be examined again during the last step D of the simulation process.
In step A of the method, a partition of the set of validated transitions is therefore made into a set of passable transitions and into a set of transitions to be examined again. Once the transitable transitions have been determined, the steps B and C of the method make it possible to activate the stages situated downstream of these transitions and to deactivate the stages situated upstream of these transitions, that is to say to continue the automated cycle.
The last step D of the process consists in re-examining the transitions likely to remain validated which have been determined in step A, indeed these transitions could have been modified by deactivating the stages located upstream of the passable transitions and no longer be validated, so that it is necessary to examine them again, in order to determine those which will be validated during the next evolutionary cycle.
In the case of a particularly complex process to automate, several distinct events and states , we obtain a command Grafcet which is complex and difficult to represent graphically, and we are, in general, led to represent this process by several "hierarchical" grafcets ", that is to say to subdivide the control law into several elementary grafcets, interacting with each other and capable of exerting actions on the operative part as well as actions on grafcets of lower functional levels.
This cutting of the control law can be done on the most varied criteria: the different mechanical parts, the different modes of on or off envisaged Cf. For example, if we consider the two grafcets G1, G2 partially shown in Figures 2 and 3 - the grafcet G1 is responsible for monitoring the safety conditions of a machine tool, such as a milling machine and comprises in particular steps II and 12 shown in FIG.
As shown in this FIG. It can therefore be seen that if, in the absence of any adequate precaution, the conditions "Emergency stop" and "Auto run" occur simultaneously during the same cycle, there is generation of two contradictory orders. However, to avoid this type of conflict, the programmer must take precautions which quickly become too burdensome with the increase in the quantities of security and other conditions external to the initial problem to be treated.
The conditional action is a continuous action, the execution of which is subject to an additional logical condition. Very often, conditional actions are timed actions, time intervening as a logical condition.
Figure 4 illustrates two conditional actions A and B, part of the grafcet of which is shown diagrammatically in Figure 5. Consequently, and as shown in FIG. These conditional actions have a "mixed" character insofar as they have two distinct components: - a condition component which has an "Input" character and must be calculated before performing a single action, that is to say before updating any "output" and, - an action component, which has an "output" character, since this action can only be carried out after the evolution of the command has been completely determined.
Another object of the invention is therefore to provide, in the case of a multiple grafcet, a method making it possible to pass directly from this grafcet to the control of the corresponding process, by allowing the coexistence within this grafcet of several grafcets, avoiding conflicts between the different grafcets that could result from contradictory orders and solving the problem posed by conditional actions.
This object is achieved in that the method according to the invention, which contains the steps A to D described above, consists in classifying the actions 12,22 by priorities and in treating these actions 12,22 in order of priority. The priorities are assigned according to the relative importance of the grafcets, so, for example, in the case described in FIGS.
This method therefore makes it possible to take into account, in a safe manner, the safety conditions in the automation systems, which is often difficult to achieve in other control systems. With regard to the conditional actions, the method according to the invention consists in evaluating the conditions of these conditional actions after having determined the active stages of the cycle and in choosing the action to be carried out according to the result of the test, the actions retained being carried out in accordance with the order of priority.
This way of proceeding makes it possible to guarantee that no action depending on the current cycle will influence the evaluation of a condition, since the conditions are only evaluated after determining the active steps and that the conditional actions will be treated as actions normal respecting the priorities and interlocks.
In order to allow the coexistence of several grafcets within the same complex control law, the method according to the invention defines four types of interactions between the grafcets - launch of the execution of a grafcet from another grafcet launch ; - complete stop of the execution of a grafcet from another grafcet kill ; - control from a grafcet of the suspension of the execution of a grafcet, this nonetheless remaining in the context of the control law and being able to start again on the user's programmed request, its active steps remaining active during the suspension of execution freeze ; - command from a grafcet to resume the execution of a previously frozen grafcet restart.
The simulation method according to the invention then consists - in step A, to calculate the receptivity only of the validated transitions whose grafcet is not frozen or killed, to place the transition in the set of transitions to be re-examined, if the grafcet is frozen, and to lose the transition if the grafcet is killed and further includes the steps of: E- determine the stages comprising conditional and active actions in the previous cycle which remain active at the end of the current evolution cycle F- determine the conditional actions that must actually be carried out, taking into account the conditions relating to the active stages of the current cycle, and taking into account the priorities.
G- execute in decreasing order of priority the actions to be performed, so as to update the outputs, these actions only being executed if the associated grafcet is not frozen and active.
The actions kill, freeze, launch are integrated by means of activity indicators in a manner known per se. This process joins the theoretical model when the cycle time tends to zero. However, the multigrafcet structure can lead to simultaneous orders and counter-orders. Another problem posed by the multigrafcet structure is that of conditional actions. CLAIMS 1- Method of automating a process directly from its Grafcet, characterized in that it consists of - freezing the information or inputs originating from the process to be automated, the freezing of each information or input being carried out only 'when this input is used during the cycle; - determine from this information the actual evolution of the Grafcet of the system - communicate to the process the new established instructions, that is to say update the outputs.
S Automation method according to claim 5, characterized in that the updating of an output is carried out only once at most during the same cycle. S Method for simulating the evolution of Grafcet according to claim 7, characterized in that it consists of.
B- activate the non-active stages located downstream of the passable transitions and transform the transitions downstream of these stages into validable transitions;. D- examine the stages situated upstream of the validated non-passable transitions determined in stage A, in order to determine those which will be validated during the next evolution cycle.
IK Simulation method according to any one of Claims 8 to 10, characterized in that in the case of a multiple Grafcet, it consists in classifying the actions 12, 22 by priority and in treating these actions 12, 22 in decreasing order of priority and to lock the "action variables" after update, this locking being achieved by invalidating the variables used, finally action.
E - determine the stages comprising the conditional and active actions in the previous cycle which remain active at the end of the current evolution cycle,. F - determine the conditional actions that must actually be carried out taking into account the conditions relating to the active stages of the current cycle, and taking into account the priorities,. G - execution in decreasing order of priority of the actions to be performed so as to update the outputs, these actions only being executed if the associated Grafcet is not frozen and active.
Method for automating a process directly from its grafcet and method for simulating the development of a grafcet. FRB1 en. JPB2 en. Process control configuration method, process control configuration system, and software system. EPB1 en. Method and apparatus for controlling a system using hierarchical state machines. USB1 en. CAC en. Method and apparatus for generating an application for an automation control system.
Multi-layer state machine for a hybrid real-time control system and method of operation thereof. USB2 en. Integrated project management and development environment for determining the time expended on project tasks. Drafting method for industrial and building systems and computer-controlled planning system for use in said method.
USA en. JPA en. Methods and apparatus to manage module run sequences in process control environment. Method for generating a monitor program for monitoring text streams and executing actions when pre-defined patterns are matched using an english to awk language translator. USA1 en.
Automate programmable cours grafcet & problèmes
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COURS AUTOMATISME GRAFCET PDF
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Cours Complet sur le Grafcet + Exercices Corrigés (1)