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Master project of Jelte Leijenaar

This is the page of the Master project of Jelte Leijenaar. This project is done for Neopost Technologies B.V. and this page is the main communication channel for this project.




On this page a short progress report will be posted every week from 14-04-09.

Progress 20-04-09

In this section I'm going to give the example mentioned in the last update. The Interface between the Feeder Vertical and the Collator is shown in the next figure.

Before the Vertical can start sending document sets towards the Collator, the Collator needs to tell the Vertical Track it's ready. This is done by the Col_ready2recieve action. After this action the Vertical Track can activate clutch VCL1 and start sending the document sets. When sensor VPH2 turns off a document (set) has been send to the Collator. To prevent collision clutch VCL1 needs to be deactivated first, before confirmation can be sent to the Collator via action VT_DS_complete. This sequence is the same for every document (set). Every space between document (sets) in the Vertical Track signals a Collator sequence. The Vertical Track sequence is shown in the figure below.

The Collator also has a relatively simple sequence. Before it can sent the ready signal to the Vertical Track it needs to set motor VM1 into the forward direction. After the Vertical Track sends the VT_DS_complete signal, the Collator can start its sequence. First it has to wait till the documents are aligned to one of the document stops. This is represented by the Col_sync signal. This is a virtual sensor, which I will describe some later update. After this signal VM1 needs to be reversed, via the VM1_stop and VM1_rev actions. The document (set) is moved towards the Fold area. When the Fold area sends the Fol_received action the document (set) is pulled into the Fold area and VM1 can directly stop and prepare for a next document (set). This sequence is displayed in the next figure

These components have a simple control sequence, which can easily be dealt with by a local controller. Therefore these sequences will be handled as it were plant behaviour. This means that the supervisor will be based on these models instead of the fully uncontrolled plant, with its sensors and actuators. The interface is a requirement which both sides of the interface need to respect. The Supervisory Control Theory can check this.
Taking the sequences of the Vertical Track and the Collator as the plant model and the interface as the requirement, the theory will try to find a controller which lets the plant behave according to the requirements. Because a VT_DS_complete action can never occur before a Col_ready2recieve action this cannot happen in the plant model. When this does happen, an empty controller will be generated by the Supervisory Control Theory. In this case both sequences respect the interface and a proper supervisor will be generated.

Progress 17-04-09

Today I had a meeting with Bert and we came to a conclusion. The ideal behaviour of the DS-86 can be represented by a so-called partially controlled plant. In such a plant simple sequences of actions are already included, making a supervisor simpler. In the case of the DS-86 a fully controlled plant can likely even be created. Making a supervisor almost obsolete. It's only going to be used to test if a new component is following the defined interfaces between the components. This way a faulty component can be detected before its implemented. I will give an example using the interface from last update, somewhere next week.

To make the plant a bit more interesting some simple error-handling will be included in the model for the Feeder Vertical. This will include detection of a stuck document and error handling. This error handling will stop the machine and let the operator remove the stuck document. Then the machine will empty itself and restart. Since that is what I noticed when an error occured. I've posted a question about it in the question section.

Right now the following things are planned:

  • The model of the Feeder Vertical will be finished, including the simulation model and the mentioned error handling
  • A simple model of the Inserter part to be able to:
  • Create an Interface between the Feeder Vertical and the Inserter using Supervisory Control
  • When there is time the Inserter will be extended with a proper simulation model and simple error-handling.

I will adjust my planning in the coming week.

Progress 15-04-09

In order to show the advantage of modelling with Supervisory Control Theory and CIF/Chi the project has made a change of direction. In stead of delivering a complete model of the DS-86, the focus is now on showing the advantages.

Because Neopost wants interchangeability the components will only have internal events/actions, except for a small communication with the neighbouring communication. This communication will be presented as an interface. This interface will be kept as small as possible to keep the level of interchangeability as high as possible. Below an example of this is shown between the Vertical Track and the Collator.

Previously the interface between the Vertical Track and Collator consisted of 4 states and 4 actions, as shown in the figure below.

To prevent collision of papers from the Vertical Track in the Collator, the Collator needs to be moving in the forward direction (VM1_for), before the Vertical Track can enable VCL1 (VCL1_on). The completion of a document set is noticed by sensor VPH2 turning off (VPH2_off). VCL1 needs to be disabled directly to prevent the next Document Set from entering the Collator. Only then the Collator can take actions to move the document set towards the Fold tables.
When this interface is used the Collator needs to know 3 actions from the Vertical Track, which makes it less interchangeable.

The new interface only consists of two states and two actions:

To prevent collision the same properties need to hold. So VM1 needs to be in a forward direction before VCL1 can be enabled. After the Collator does the VM1_for action, it can perform the ready2recieve action. This lets the Vertical Track know it can enable VCL1 and start transferring a document set towards the Collator.
When in the Vertical Track the action VPH2_off is detected clutch VCL1 is turned off. Now the action ds_complete can be performed to let the Collator know the document set is ready.
With this interface the components only have to keep track of 1 external action. But it does have one more internal action to keep track off. This means that the supervisor may increase slightly in size. In exchange of this small increase in size the interchangeability is greatly improved. One of the components can be replaced with another as long as it follows the interface.

NOTE: This is the interface without the Shunt function. This function will be in the final interface between the Vertical Track and the Collator

twins/master_jelte_leijenaar/progress.txt · Last modified: Monday, 20 April 2009 : 13:37:30 by jelte.leijenaar