This study was conducted to determine the optimal performance of automated log-rotation systems that are integrated into most softwood sawmill canter infeed systems.
The study was conducted on a quad roll log turner mounted in front of an SLI (single length infeed) type canter infeed. A first test served to determine the log turner’s initial performance and to determine the main sources of log rotation error. Mechanical modifictions were subsequently made with the collaboration of the equipment manufacturer. These modifications were followed by a second performance test. Certain improvements were noted, especially with respect to post-rotation log positioning. A second set of corrective measures focused on improving log turner rotation accuracy prior to conducting the final performance test.
Initially, the standard deviation (SD) for the the study system’s rotation error was 36 degrees. After two sets of technical corrective measures, the SD with respect to log rotation accuracy dropped to 24 degrees. In order to achieve this level of accuracy, certain mechanical components were modified and others were replaced due to wear. PLC programming was also reviewed in order to more effectively synchronize pressure roller sequencing and to preposition the log rotation rollers. A simulated rotation improvement from a standard deviation of 36 to 24 degrees represents increased benefits of 2% or $2/m³ for the study sawmill. The improvement potential would have been double, however, if the SD reflecting the rotation error could have been brought down to 10 degrees. Rotation accuracy could likely have been further improved, however, this would have been difficult to achieve and maintain with current technology.
In the future, manufacturers should focus on the development of new types of equipment capable of achieving better results, especially for processing small-diameter logs at high speed. Furthermore, log turners would benefit from the addition of continuous monitoring and control systems to ensure optimal log position at all times. Moreover, self-correcting, closed-loop systems would also improve the performance of roller-equipped log turners.