In a digital printing apparatus, such as an inkjet or laser printer, an image pipeline is used to convert an image to be printed into instructions or data that are used to control an image writing mechanism, such as an inkjet printhead or laser writing mechanism.
For a printer to accurately print an image on a substrate the substrate has to be both accurately aligned relative to a predetermined axis, such as a printing axis, and be accurately positioned relative to a predetermined reference printing position. The printing predetermined axis may, for example, be defined as an axis of relative movement between an image writing mechanism and a substrate within a printing apparatus.
If the substrate is not accurately aligned to the predetermined axis, the printed image will be printed skewed relative to the substrate. If the substrate is aligned with the predetermined axis but is offset relative to the predetermined reference position, the printed image may, for example, be printed partly on the substrate and partly on a printer substrate support, or the image may otherwise not be located in a desired location on the substrate.
Accurate positioning of the substrate may be achieved using various techniques. For example, some printers use one or multiple accurately placed mechanical substrate guides, against which a substrate is placed, thereby helping to ensure that the substrate is both correctly positioned and correctly aligned. Other printers may include mechanical registration pins, stoppers, or the like.
Accurate substrate positioning becomes increasingly important as substrate size increases. For example, with a 1 meter wide by 3 meter long substrate, even a slight misalignment can lead to a noticeable skew of the printed image, potentially leading to the print being unusable, leading to waste of both substrate and ink, and reducing printer throughput.
In some printers, a human operator may load a substrate into a printer. The operator is responsible for ensuring the correct alignment of the substrate. However, the use of a human operator to accurately load substrates is generally time-consuming and costly.
In other printers, substrate loading mechanisms may be used. However, such loading mechanisms have to be able to repeatedly load substrates with a high degree of precision. However, such mechanisms add cost and complexity to printers.