SAWLINES – DELTA COMPUTER SYSTEMS
LUMBER PROCESSING
Figure 2
Getting past starting friction
The Sciere LaPointe & Roy line includes canters , profilers and gang saws manufactured by PHL with optimizing and motion programming by Prologic +
Motion controller solves ‘ stick-slip ’ problem for Quebec sawmill gang saw . By Bruce Coons , Delta Computer Systems
The new curve-sawing line at the Scierie Lapointe & Roy softwood mill in Courcelles , Quebec is a technical marvel . The mill ’ s curve saw line employs a bank of five electrohydraulic motion controllers by Delta Computer Systems of Battle Ground , Washington to achieve the smooth coordination of more than 30 motion axes .
“ We selected the eight-axis RMC150 motion controllers from Delta ( see Figure 1 ) because of the flexibility they provide and because they are well-known controllers in the wood industry ,” said Francois Giguere , Wood Process & Optimization Specialist at Prologic + of Saint-Georges , Québec , the integrator of the mill upgrade project .
“ We ’ ve been using Delta motion controllers for years and have found their software to be very user-friendly .”
To program the motion , Delta Computer Systems provides a free software package called RMCTools to support its motion controllers . After the motion program for each axis is developed , the motion is tuned so that the physical system functions as desired .
“ We tune each axis independently ,” said Giguere . “ The first step is usually to do the automatic tuning using Delta ’ s Tuning Wizard tool ( part of RMCTools ). After that we adjust the control loop gains if necessary to perfect the motion .”
The ‘ stick-slip ’ problem Delta ’ s Plot Manager , another component of RMCTools , was used to monitor how the actual motion differed from target motion during an operational cycle . It was using the Plot Manager that the Prologic + team identified a problem with tuning the motion of the gang saw wiggle box .
“ The wiggle box moved on a smooth oil bearing , but it wasn ’ t smooth enough ,” said Delta President Peter Nachtwey , who helped with the axis tuning . “ Making the problem worse was the small diameters of two of the cylinders that move the box .
“ As a result , the system had a low natural frequency and was not as ‘ stiff ’ as it should be . This made it more susceptible to stick-slip .” When the wiggle box was moved quickly between cants , the problem didn ’ t manifest itself , but during the curved sawing of boards , the motion from side to side and angle changes were relatively slow , so vibrations could be felt by touching the machine and easily seen on the plots . The vibrations affected the precision of the cuts and could cause maintenance problems if allowed to continue .
The solution To overcome the friction problem , Delta ’ s Nachtwey recommended that the Prologic + engineer tune one of the control
Figure 1
algorithms operating the wiggle box to increase the gain of the acceleration parameter , which gave more power to the actuator at the start of each move operation .
“ The second derivative gain is
applied to the error between the target and actual accelerations ,” said Peter Nachtwey . “ Secondorder tuning helps a lot to overcome the effects of stick-slip .”
The actuator tuned up easily after changing the tuning to acceleration control using the Delta ’ s auto tuning procedure . The tuning process took less than 10 minutes .
“ The new automated sawline ( Figure 2 ) has increased the mill ’ s production by some 140 % in board feet compared to the old mill that burned ,” said Giguere . “ And the new mill is safer and easier for the operators to run .”
The RMC150 motion controller can control and synchronize the operation of up to eight motion axes simultaneously
18 International Forest Industries | AUGUST / SEPTEMBER 2018