Our PLCs in action

By Jeremy Pollard, CET, Columnist

In February, I wrote Control Design’s anniversary piece on the evolution of the PLC over the past 10 years ["Back to the books: PLC easy reader"]. I thought now it would be a good idea to see what’s actually put into practice these days. I was led to a small OEM in the lumber industry that embodies the evolutionary existence of the PLC.

Daqota Systems, based in California and Minnesota, builds X-Y scanning systems for veneering operations at major wood suppliers. Its systems maximize the available veneer its users can harvest from a given log. This can eliminate problems with knots in the log, and makes sure good wood is reached before turning and extracting the veneer.

Basically, a log comes into a carriage, and is scanned by Daqota’s systems. Once the algorithms execute, a very long knife penetrates the surface of the spinning log, and a ream of wood is expelled like an apple peel.

Constant thickness requires constant speeds and constant monitoring. Daqota provides two systems: a single-point laser system using two to 16 single-point laser scanners, and a second system that employs up to four line scanners to provide the equivalent of 1,000 single-point lasers, both of which digitize an eight-foot log with up to 500,000 points.

The optimization required for this process is part of the value Daqota adds to its systems. They need speed, and computing power to do it.

High-speed analog inputs are employed for the single-point laser systems, which are inserted directly into a ControlLogix backplane. Al Woodward, vice president of Daqota, says the hardware finally is fast enough to perform the calculations needed for their optimization techniques. The math required by the single-point system can be done in the processor. This PLC solution is real-time enough for them. The line scanners and all system components are connected by Ethernet.

In some cases, there still is waste, but the line scanners create a level of optimization that Woodward says gives customers everything the log can give, and also provide more accurate positioning of the carriage to reduce cycle times.

The data from the controller and the line scanners are tied together with a Visual C# application, which can generate the required algorithms very quickly. The data to and from the controller is accomplished using a Daqota custom driver as well as a .Net component from Automated Solutions. I’ve used their ActiveX controls, and know them to be fast. Woodward says the throughput of the driver has no impact on their solution.

The C# application coordinates the data from the controller and the line scanners using the .Net communication control, and then tells the controller to get it done.

Using the data from the scanners and the controller, a Daqota-built 3GL HMI system can show an operator in real time how the log looks and what the optimization structure looks like. Historical views are available.

Data collection is done via the network to a SQL database.

Speaking about integrated motion control, Woodward also says, “Now we can provide systems that are tightly integrated, easily accessible for our customers, with hardware that is supported worldwide.”

Seven or eight years ago, Woodward adds, the hardware and software weren’t available to perform the level of control that  Daqota and its users are experiencing now. It’s because of the hardware that they’ve been able to set themselves apart. Tim Woodward, president of Daqota, concurs, saying, “Previously, we would have to integrate additional PC-based or standalone motion controllers and integrate them with a PLC for the most demanding applications.”

The advancement of networking, driver software, .Net, data collection capabilities, and the raw speed of available devices allowed them to produce a system that saves customers dollars on their raw materials and dollars on their finished goods.

The integration of motion and sequencing, and the software to tie it together, allowed this OEM to evolve as the PLC has. And both Woodwards like the no-cost runtimes for their HMI.

This indeed is one of those cases in which the user actually agrees with and is implementing everything its vendors were touting. Some would suggest that he could have used a PAC, but isn’t the ControlLogix a PAC? Once again, it depends on who you ask.

In any case, it’s PLC evolution.