6.Places - larics/Petri.Net GitHub Wiki

Toolbox window under Simple section contains five types of Place objects. They are: Input, Operation, Resource, Control and Output. They all have the same common properties:

  • NameID : name of the place (user defined),
  • Location : Location of Place object within PetriNet Editor object,
  • Tokens: number of tokens in the place; defined at the beginning of the simulation represents initial condition, during the simulation this property changes as the number of tokens change.

Figure 6.1. Common properties of Place object.

Input Place has one additional property, InputType, that is required for setting it's behaviour. By changing it's value two additional properties can appear (Interval and RandomInterval). That property can have three values (shown on Figure 6.2):

  • Fixed: Input object has fixed number of tokens determined by initial condition; Tokens can only go out of Input object they cannot come in (from external buffer)
  • Periodic: Input object gains additional token after n steps of simulation; n is determined by additional Interval property
  • Stochastic: Input object gains additional token at random steps. Random numbers are generated from interval [1, RandomInterval], where RandomInterval is additional property that will be shown if Stochastic value is selected. The greater RandomInterval value is, the rarer will tokens arrive at Input object.

Figure 6.2. InputType property of Input Place object.

Place properties depend on PetriNetType property of PetriNet Document object. If PetriNetType is TimeInvariant then all properties used for definition of time dependent parameters are hidden.

If PetriNetType property of PetriNetEditor is PTimed additional property appears (for Places described as Operations or Resources):

Operation Place

  • Duration: processing time; length of the operation in sample time units,

Resource Place

  • ReleaseTimes: this is a set of values that determine how much time (in sample time units) resource needs to become idle after finishing each of its tasks (operations).

Figure 6.3. shows a PTimed Petri net model with shared resource (place MA). Shared resource is capable of doing more different operations.

Figure 6.3. Petri net model for multi-operational resource.

The model contains two input places (IA, IB), two operation places (M1P, M2P), two output places (OA, OB), one resource place (MA) and two control places (UD1, UD2). Each place has name, shown in the upper part, index, shown in the lower part and the number of tokens, shown in the central part (black dots or an integer in case the number of tokens is >4). In case place MA is selected, click on the button next to the ReleaseTimes property in Properties window (Figure 6.4.) will open a new window shown in Figure 6.5.

Figure 6.4. ReleaseTimes property.

Figure 6.5. ReleaseTimes editor window.

In this window release time for each operation associated with selected resource is determined. Release times are defined in sample time units.

Another special Place object that needs to be explained is Control Place object. It is drawn with double circle so it can be distinguished from other Place objects. Control Place is like any other Place object except that it's Tokens number can be controlled by Rules. This is only a brief explanation, more detailed explanation is given in "Rules and Rules Editor" chapter later in this manual.