Dynamic focusing method and apparatus

A method for focusing a camera on a moving surface of variable geometry comprising:

• identifying a location on a sample surface as an origin, the sample surface being substantially similar to the moving surface;
• measuring the location of a predetermined number of points on the sample surface relative to the origin;
• generating a model of the shape of the sample surface using the location of the points and the origin;
• measuring the location of a predetermined number of points on the moving surface;
• fitting the model of the shape of the sample surface to the moving surface using the locations of the predetermined number of points on the moving surface such that the distance of that portion of the moving surface presented to the camera at a predetermined time is known to within a range of distances that is within a depth of focus of the camera;
• and
• driving the camera to dynamically maintain the moving surface within its depth of focus using data from the model fitted to the moving surface.

An imaging mechanism for capturing images of a moving surface having a variable geometry comprising:

• a camera for capturing images;
• a focusing assembly that defines an optical path between the moving surface and the camera, the focusing assembly including a prism adapted for substantially parallel movement toward and away from the moving surface, the distance between the prism and the moving surface being related to the depth of focus of the focusing assembly;
• and
• an illuminator for illuminating the moving surface.

An imaging mechanism for capturing images of a moving surface having a variable geometry comprising:

• a camera for capturing images;
• a focusing assembly that defines an optical path between the moving surface and the camera, the focusing assembly including a prism adapted for substantially parallel movement toward and away from the moving surface, the distance between the prism and the moving surface being related to the depth of focus of the focusing assembly;
• an illuminator for illuminating the moving surface;
• and,
• a sensor for determining a distance between the moving surface and the focusing assembly, the distance data captured by the sensor being used to drive the focusing assembly to maintain the moving surface within the depth of focus thereof.