Safe and fully integrated industrial chainsaws

Industrial saw maker gains precision, safety and serviceability with advanced, highly integrated fail-safe PLCs, drives and other components

By Victor Gonzalez, Charter Controls

Since 1996, Pacific Trail Manufacturing has provided a wide range of crosscut saws to help customers to process milled or engineered wood products with the least time and labor. Its industrial chainsaws can process full units of lumber, plywood and other wood types to length and to a variety of tolerances—as precise as 1/64 of an inch or 0.4 mm. Typical customers include lumber remanufacturers and makers of pallets, as well as trusses and studs for residential housing.

“Any company using high volumes of cut-to-length wood products can benefit from our specialized saws,” says Tom Langton, president of Pacific Trail Manufacturing. “They produce consistently precise cuts, despite variability in the wood feedstock, which can be dry or wet. If it’s the latter, a pallet of feedstock can weigh up to 20,000 lb, but our saws can still position and cut to our customers’ precise requirements.”

Based in Portland, Oregon, Pacific Trail builds saws that are in high demand around the world, even at a wood products depot in largely forest-free Kuwait. But, despite its success, the company has remained purposefully small. Its staff is just 10 people, including Langton, who also handles sales, and co-owner Bruce Wold, who manages engineering, installations and service.

The challenge was to boost the precision performance, safety and serviceability of the company’s flagship Accu-Cut industrial cross-cut chainsaw (Figure 1), which is its most sophisticated saw and operates with the automated precision and control of a computer numerical control (CNC) machine, says Langton. “The Accu-Cut is more like a CNC than it is some giant version of your backyard chainsaw,” he says. “It can be programmed with up to 20 different recipes, each with 10 different cuts. Most of our customers average between 80 and 100 cuts a day.”

One of the Accu-Cut’s hallmarks is its gear-and-bar conveyance system that can precisely hold and position tons of milled lumber or wood products for exceptionally precise cuts. “Competitors use hydraulics or chain-drive mechanisms, but those can’t match ours for speed, performance and reliability,” Wold explains. “What might take three workers 45 minutes with other saws to process takes just one worker 10 minutes with ours.”

Langton further illustrates why consistency is so important to Pacific Trail customers. “With a unit saw, you can create 200-plus 925/8-inch studs in under two minutes. But if the cutting tolerance of the saw isn’t consistent in holding 925/8 inches, you’ve created a finished product very quickly that you can’t use or sell.”

Uptime is another hallmark of the Accu-Cut saw. “Since the Accu-Cut has fewer wearable parts, customers experience little or no downtime due to the saws themselves,” Wold says. “That’s important because downtime isn’t an option with our saws being indispensable machinery in our customers’ production. That’s why we design, engineer and build our saws to be as reliable and easily serviceable as possible.”

Upgrade safety and control

For Accu-Cut saw’s controls, it turned to long-time partner, Charter Controls, based in Vancouver, Washington. The saw has a chain-driven carriage. Because the long chain length is susceptible to stretching and slack, synchronizing the drive with the mechanical system was very challenging, especially when a pallet of wet lumber can weigh up to 10 tons.

The Accu-Cut saw’s control system was due for an upgrade, having relied on aging third-party PLCs, drives and separately wired safety relays for more than a decade. If any of those components or supporting wiring would go out, a customer’s production could be down for days, while the staff troubleshoots the problem with Pacific Trail and Charter Controls providing phone support.

A big reason for that is the general wiring of safety relays, which can be complicated and confusing. Meanwhile, the lost production can add up to tens of thousands of dollars a day, not to mention the missed delivery commitments and resulting order backlog.

The solution

Being familiar with the Accu-Cut control panel, Charter Controls recommended upgrading to a new Siemens PLC with integrated safety and remote diagnostics, plus drives, HMI and supporting components. Working closely with Pacific Trail’s Wold and its design engineers, Charter Controls designed and built an entirely new control system for the machine, driven by a 20-horsepower ac motor. The local branch office of WESCo Northwest Automation provided components.

Having fail-safe features already in the Simatic PLC greatly simplified the panel’s design, and its small size saved panel space. And, by eliminating safety relays, which require a lot of complex wiring, it also makes panel manufacturing easier.

Troubleshooting is much easier through the use of integrated diagnostics that can be remotely accessed. In the past, if a customer had a problem with the saw, such as a safety relay failure, they would call Pacific Trail, which would escalate it to us, if necessary. All that would consume considerable time while production has ground to a halt. Now we can connect to the PLC remotely and view the program to know exactly which circuit needs attention, saving significant time.

In addition to upgrading the PLC, the full solution from Charter Controls also included variable speed drives and a new human-machine interface (HMI).

A Sinamics S120 drive is used to precisely control the positioning of the Accu-Cut saw’s carriage, even under tons of weight, while a compact Sinamics G120 drive controls the saw bar (Figure 2). The combination of these two drives worked well. The S120 is designed for high-performance, motion control applications. And the G120 saves space and has its own safety-integrated features to complement those of the Simatic Safety PLC.

Mounted to the cabinet for the Accu-Cut saw is a nine-inch Siemens Comfort Panel HMI display. Its color touchscreen provides plenty of area for operator information and controls interaction. The more information we can provide operators, the better they can manage the saw. This results in less support calls to Pacific Trail and, if escalated, to us with questions. In the past, this took up a lot time, which is now drastically reduced.

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Software platform

The Charter Controls solution team used the Siemens Totally Integrated Automation (TIA) Portal, a software engineering framework, to program the PLC with the Accu-Cut saw’s many recipes and safety features. The saws use Safe Torque Off to stop the motors during emergency stops.

The TIA Portal reduced our PLC and HMI software programming time, often by as much as 30%, saving us days, if not weeks. The function libraries that come with the TIA Portal, along with the programming diagnostics, are big time savers. We can also save our own code for reuse in other applications, which extends the value of time invested in original software development.

Safe, precise results

If Pacific Trail’s Accu-Cut saw is anything, it’s precise in its cuts. Wold points out that while the saw’s specifications state that it can cut to 1/32 of an inch or 0.8 mm, actual performance can be accurate to half that. “But just as important as precision is the consistency of that precision,” he says. “Our customers’ feedstock can vary a great deal, not just from one pallet load to another, but also from board to board or sheet to sheet."

The combination of the Siemens Simatic PLC and Sinamics drive is valuable. "By working together, they can monitor motor current as an indicator of wood conditions and adjust the blade speed to those conditions,” says Wold. "For example, if the motor starts drawing over 15 or 16 A, the saw can slow down by as much as 50%, adjusting the cutting speed automatically to keep the cut precise.”

Overall, the Accu-Cut’s new control panel from Charter Controls has helped to improve the safety and serviceability with the advanced PLC’s integrated safety and remote diagnostics. While the former is critical for the Accu-Cut’s safe operation, the latter is important for both Wold, as first-line support, and me, as the escalation point.

On this, Langton agrees wholeheartedly. “Having Siemens components inside Charter Controls’ panels helps to make our Accu-Cut saws sell themselves,” he says. “And, like any salesperson, I’d rather be taking orders for our saws versus making sales any day.”

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