FBD is a method of programming that compartmentalizes and hides code within boxes called function blocks. These function blocks display only the inputs and outputs of the compartmentalized function and can be implemented repeatedly throughout a larger program.

Benefits of using FBD code:

• Function blocks can be more intuitive for those with electronic/computer science background as FBDs are comparable to logic gates
• FBDs be much more compact than a ladder for logic with lots of components
• FBDs allow for compartmentalizing complex code into a simple visual block
• FBDs enable users to modify repeated code within blocks only once; changes to a function block propagate to all instances of the function block

Drawbacks of using FBD code:

• FBDs can be unfamiliar, and therefore more confusing, for developers or maintenance staff as ladder is generally a more commonly-used programming language
  • NOT nodes are especially small and can be easy to overlook
• Compared to ladder, FBD can be less intuitive for those with electrical backgrounds as ladder logic is based on circuit diagramming for relay logic
• Like Ladder Logic, FBDs don’t support complex math sequences or functions
  • Structured text is more useful for this
  • With that said, structured text is supported when programming in FBD

“AND” and “OR” Operations in Ladder Logic vs. FBD

In addition to programming in FBD, other considerations DMC took into account were:

• I-Device communication
• Safety programming

The plasma treater we were programming was only one step in a much larger operation. As a result, the treater’s PLC served as a slave to a master PLC that controlled the overall system process. DMC configured I-Device Communication between the two units utilizing a PNP coupler to allow signals to pass from slave to master and vice-versa.

The plasma treater project marked the first time DMC’s clients had utilized failsafe logic in their products. DMC was able to provide insight on best safety practices and Siemens-specific safety concepts to our clients. Specifically, DMC successfully incorporated logic that allowed for safety bypass modes when the plasma treater needed to undergo maintenance.

Learn more about DMC’s work in the Food and Beverage Industry and our Manufacturing Automation and Intelligence Services.

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The PLC communicated to the servo controllers using a serial connection through a Siemens CB 1241 RS485 serial interface. Each serial message consisted of several parts: a start signal, a device address, a function command, an error field, the results of the function, an end signal, and a checksum. The PLC would take the setpoint from the HMI and format it as a serial message to the correct drive. It would send the message over the serial port, wait for a response, and process the response into the correct data. All serial messages were sent and received using standard Siemens instructions. Any communication errors would trigger a warning on the HMI to notify the operator.

The serial architecture was set up with the PLC as the master, and the controllers as the slaves. As a result, the controllers would not send data until the PLC asked for it This eliminated the need for monitoring the serial channel, streamlining the communications. However, this setup does require the PLC to send data to one controller and wait for a response before sending data to the next controller. This might render a larger system may susceptible to communication delays, but the effects were negligible in this system with only two controllers.

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Database

The database serves as a central repository for all label configuration data. It is a Microsoft SQL database stored in an on-premise server to ensure continuous stable connectivity from the desktop application and web application. The database schema was designed to support change tracking, so the edit history of any given label can be retrieved and viewed. In additional to label data, the database stores records of all batch printing jobs initiated by the desktop application.

Desktop Application

The desktop application allows operators to manage and initiate batch label print jobs. Users log in to the application with the same Active Directory credentials they use to log in elsewhere in the company network; once the credentials are verified, the application checks the database to determine if the user has access to the application.

Use of the application centers around the management of new print jobs. Users can switch between existing print jobs and add new ones by using the tabbed interface along the left side of the screen. Users may also view a summary screen showing detailed information on all active print jobs.

Creating a print job follows a simple and straightforward process. Users first enter a material number located on the bill of work for the print job they will be initiating. The application retrieves all label artworks associated with that material number and places them into a dropdown for the user to select from. Once an artwork is selected, read-only information pulled from the database is displayed on the right side of the screen so the user may verify they have selected the correct label artwork to print.

Additionally, a list of variable data parameters that need to be filled in for the selected artwork appear. The user must provide data for all of these parameters. Indicators next to each field let the user know what sort of data needs to be supplied for each parameter (e.g. the Expiration Date parameter requires a future date) and whether or not the entered data is valid. Once all data has been entered correctly, the user may generate a print preview to verify the label is formatted correctly.

The final step is to select a printer. This brings up status information about the selected printer (such as whether it is idle, currently printing, in an error state, etc.) and allows the user to bring up the print preferences dialog to configure any printer settings. The user is also allowed to print sample labels as a final check to make sure everything is correct. Once the user is ready, they fill in the number of labels to print and initiate the job. All fields and dropdowns are locked until the print job completes or is manually stopped. 

Web Application

The web application serves as a front-end to the database, allowing for the creation, modification, and management of labels. This includes managing the label stock that labels are printed on, the artwork defining what the labels look like, and the products that the labels are for.

The web application automatically grabs a user’s Active Directory credentials to log them in. The actions a user can take as well as the portions of the web application they can see are tied to their permissions. By default, users can only view label data. Users with administrative privileges can grant additional permissions to any user, expanding their list of capabilities to modifying label data, approving label changes, and uses the desktop application to print labels.

When a record is changed, it moves from an “Approved” state to a “Pending” state. No more changes to that record can occur until a user with approval permissions either approves or rejects the changes. Until that happens, the desktop application uses the latest approved data for any print jobs that are initiated. To facilitate the approval process, users can view a side-by-side comparison of what changed in a “Delta V Report”.

Since some users may wish to request a change without having the permission to do so, a “Change Request Form” can be accessed for any given record. This lists out all the data tied to a record with a second column where the user may type in their desired changes. They can then save or print a printer-friendly version of the form.

To make creating brand new records easier, a “Copy From” feature allows users to begin creating a new record with another record’s data as a template.

Viewing the potentially large quantities of records is simple with the ability to quickly sort and filter grids on any column.

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Some facilities use several of these tax stamping machines at once, and that demands proper maintenance. This requires having the correct machine settings on each machine, and this can be done by copying the settings from one machine to another using a USB stick. DMC made this process more robust by modifying the B&R code to perform searches in order to confirm that the correct settings are written to the correct variables.

It is most important to make sure that the correct stamps are applied to all the products that go through the machine. After hours of continuously running the machine, some of the stamps can become misaligned. DMC implemented code to check the stamp paper before moving it to make sure the stamps are still aligned with the stamper.

Learn more about DMC’s B&R automation studio programming services.

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