Label Center Checking
It is a known fact that using a camera to measure the centeredness of a stick-on label can be difficult. In this case we are referring to product that is typically oblong or has a near flat front surface. Typically bottle position and orientation are not very repeatable as they exit the labeler. Thus as the bottle moves down the line there will be variation in in/out position and the rotational aspect of the bottle, with respect to the camera. Here at Decision Technology, a company specializing in machine vision solutions, we have developed a new algorithm that determines a “Goodness of Center” factor which is proportional to how well a label is centered even thru a reasonable amount of positional ambiguity of the bottle. This typically includes:
- in/out position (tested up to +/- .05 inches)
- rotational variation (tested up to +/- 3-degrees)
We believe that the algorithm will work with over a larger degree of variation but have not tested it as of yet. This measure can then be used in conjunction with a set of min/max allowances in regard to a judgment for ejecting the product. Given appropriate lighting, the technique is compatible with both solid and translucent labels and bottles. It is also compatible with a wide range of camera resolutions.
The following test results are provided. It is our opinion that an allowed “Centeredness” value of between +/-15 would work quite well at providing a “Good Judgment” range. Of course the system can also detect vertical rotation of the label, with additional image processing methods.
|of centeredness value|
|0 deg rotation||centered||0.214||53.58||4.38|
|CCW 3.0 deg||centered||8.054||64.1||13.694|