How to cut costs and maximize production with servo automation
Inside Machines: Lumber machine manufacturer’s moves to servo control yields increased precision, productivity.
A 2x4-ft. piece of lumber is the construction industry's ultimate commodity, which is why a leader in the lumber industry is using sophisticated automation to gain a competitive advantage for this price-sensitive product.
Creating a solution with automation
WaneShear Technologies creates the sawmill machinery that puts a finished edge on dimensional lumber to create straight, clean, high-grade 2x4-ft., 2x6-ft., 2x8-ft., and larger boards. The equipment created by WaneShear's Ukiah, Calif., location has the challenge of processing this consistent product from rough lumber that was sawed from raw logs, which can vary widely in width and length before entering the edging machinery. The technical challenge increases because of the constant need to increase production volumes made necessary by the pressure to maintain profitability amid fluctuating prices in the volatile construction industry.
While automation has been part of this equation, WaneShear has been pioneering a different solution. Traditional edging automation equipment used hydraulic components. Hydraulics deliver the powerful, high torque output the application demands but often result in leaks of hydraulic fluid. Spilled fluid can damage the lumber and make it unacceptable for sale. Fluid also can combine with sawdust to create a sticky substance that gums up machinery and makes cleanup difficult.
"We knew that by switching from hydraulics to servo automation, operators could solve a lot of our problems," said Ron McGehee, president and chief designer of WaneShear's equipment and the holder of 25 plus patents on sawmill related inventions. "In the past we didn't look very carefully at servo automation because we felt servos wouldn't have the torque strength to get the job done, and they would be too large to fit in the physical space of our machines without a lot of re-engineering."
This attitude changed in the last few years, as the footprint of servo motors has been reduced and new, more powerful servo motors have come into the market.
"The time had come for a new approach, and we saw the opportunity to be an industry leader," said McGehee.
Servo automating for edging
Servo motion also offered an opportunity to improve the precision of WaneShear edgers, which would lead to more usable boards from every log. WaneShear pioneered the use of vision systems and variable frequency drives to stage rough boards for edging. The staging of boards is especially challenging because squaring an irregular board doesn't always call for a perfectly straight cut. Cutting angles can often vary by 6 deg, requiring the use of precise camming routines that often must change quickly to compensate for a variety of board contours. Because board lumber is quality graded, a better quality of cut means the machine's output can be sold at a higher price.
The edgers manufactured by WaneShear must be integrated with the other equipment in a crowded sawmill, which presents a separate set of challenges for automating the edging process. Each edger is customized to fit the available space on a sawmill floor that is filled with a variety of other equipment, which makes minimizing the footprint of each machine critical.
"Linking machines in tight spaces gets to be pretty much essential," said McGehee. "If we can replace gearboxes and hydraulic equipment with servos in the same physical space, we can add capability without adding an integration problem for our customers." Control system integration is equally important, with most mills using PLC-focused control architecture for their production equipment. "PLCs are the customer's comfort zone," said McGehee. "Whatever automation you add, it must integrate with the PLC in a way that gives a minimum of trouble for the personnel on the sawmill floor otherwise they won't buy into it."
Reliability was the primary concern and requirement for WaneShear when considering the switch to servo control. Sawmills must run around the clock, 365 days a year to remain profitable. This desire for reliability led McGehee and the other members of the engineering team to a motion automation manufacturer providing reliable servo motors and engineering support for challenging applications.
Vision system identifies target
Application technical challenges began with the staging of boards for cutting. The edger's vision system extrapolated each board's position into four position points, which were translated by a motion controller into more than 1,000 positioning points. The motion controller's cam editor tool was used to create a set of motion profiles, which were used by servo-based conveyors to precisely stage boards for the most accurate edging possible with the least waste.
The interface between the PLC and servo axes was simplified by the addition of servo amplifiers that can be controlled using the add-on-instructions from a standard PLC. This feature proved to be particularly important for the WaneShear software development team to avoid requiring customers to learn an entirely new programming interface to successfully integrate the new servos.
Integrating servo motors
Integration of the servo motors themselves proved to be one of the most positive outcomes in the development process. The servo motor dimensions made them an easy fit into the spaces once occupied by hydraulic components. The torque ratings of the motors suited them well to conveying lumber at the high-power, low-RPM rates needed by a sawmill application. The torque density profiles of the servo motors also made it possible to replace a gearbox on one of the WaneShear machine designs, resulting in cutting component costs. The precision of the motion control components allowed WaneShear to reduce errors on its conveyors from 1/8 in. down to 1/250 in., allowing the company to shorten the length of its conveyor belts without compromising the accuracy of the cut.
The servo motor implementation allowed the edger to reach performance targets. The goal was to increase output to 75 boards per minute, requiring a cycle time of 800 milliseconds per board. The design team also expected to improve the quality of boards due to the extra precision of the servo-driven control system. All targets were exceeded. Board output quality increased by 25%, and the new WaneShear servo-equipped edger is processing standard 8-ft boards at more than 20 ft per second, well beyond the 800 millisecond goal.
"We've been so successful," said McGehee, "that now the rest of our customers' plant equipment needs an upgrade to keep up with the edger ... which used to be the other way around."
The servo motors and drives used are being designed into all WaneShear machines going forward. "We are also seeing other machines within our customers' mills using the [servo] products." McGehee anticipates continuing to use the automation technology provider "for a long time to come."
Hunter Stofferahn is the regional motion engineer for Yaskawa America Inc. Edited by Emily Guenther, associate content manager, Control Engineering, CFE Media, firstname.lastname@example.org.
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