Posted on December 13, 2016

Lineal or transverse: Facts versus Fiction

When it comes to the selection of an auto grader, the initial consideration should be the debate between lineal versus transverse, as opposed to which supplier to choose from. Therefore, we will leave it to the supplier to present the advantages of their solutions over those of the competition, to their potential customers. This article will address the intrinsic engineer aspects of lineal versus transverse. If you believe in facts and science, please read on.

The first point to consider is the real estate. Is there enough available space or will the project require major adjustments to the planer layout, thus driving the total cost of the project way up. A lineal configuration will often limit those additional investments. Conversely, the mill layout may already be set up in a way to make it practical and seamless to integrate a transverse configuration from inception.

All respectful vendors, whether lineal or transverse, propose a combination of 3D, Vision and Tracheid scanning to the wood producers. The quality of their optimization, aside from their respective algorithm, depends on their capacity to collect the board data to render the best judgment on each board. A limiting factor to capture this data in a transverse configuration is the chain race blocking a defect that could prevent the right optimization of this board.

Along the same lines is the inherent simultaneous scan of the four faces by each of the three types of scanning heads, versus the limitation of the transverse scanning only two faces at 90 degrees for the 3D head and an attempt to view four faces at 45 degrees with the top and bottom tracheid and vision heads. One can see that using one camera at 45 degrees to scan two faces will inevitably result with blind spots in the wane for some cases (see fig 1). A wrong solution can result if defects like rot or splits are in these blind spots.

Figure 1

No one needs to bring to your attention the fact that chains stretch through their lifetime thus potentially causing reading issues with the width and wane in a transverse configuration. Another factor that plays in the quality of the scan is the amount of vibration; many factors can be a cause of vibration in a transverse solution, i.e. extreme bow on a board. Whereas in a lineal configuration, a top of the line supplier will either propose a set of rolls or a bridge to limit this issue. Making synchronized differential measurements with perfectly aligned sensors in a lineal system will also eliminate errors due to vibration and/or board movement.

Let’s take a look at the vision side of an auto grader for a moment. This will not come as a surprise to anyone who has ever taken a picture or a video; the rendering of the image, aside from the quality of the camera, is dependent on:

• the source of light
• its type (LED or not)
• its quality
• its capacity to maintain its intensity i.e. avoid degradation through time and ability to provide it equally to each head without the impact of the ambient light
• the sun (open door), cloud or the weather

A lineal solution, due to its enclosed quarter and disposition of the head (simultaneous reading at 90 degrees to each face of the board), will do a better job versus shedding lights along the length of your random length production (16, 20 or 24 feet).

There is a known concept in engineering; the less parts there are the less probability of experiencing a failure. There is no doubt that a lineal solution offers a major advantage in that respect, i.e. for a 16 foot random length, a lineal configuration will have a total of 10 to 12 scanning heads for the 3D, vision and tracheid sensors, versus up to 32 in a transverse 16 foot configuration. Therefore, someone should also consider that a change in scanner technology will prove less costly if there are less scanner heads to replace.

Finally, from an operations point of view, safe and quick cleaning (less scanner heads) as well as calibration (the handling of a 2 foot calibration bar versus a full length per your longest produced dimension) will prove to be a time savings and a gain in your production window with a lineal configuration. One should also pay attention to the time it may take to address a planer issue and the loss of value within your accumulation section of your planer layout.