BACKGROUND

Systems and methods herein generally relate to belt transport systems that transport sheets of media, and to sheet detection systems; and, more particularly to a sheet detection circuit that uses electrical elements contacting a conductive vacuum belt.

Vacuum belts are often used to transport sheets of material, such as sheets of paper, plastic, transparencies, card stock, etc., within printing devices (such as electrostatic printers, inkjet printers, etc.). Such vacuum belts have holes, openings, perforations, etc., that are open to a vacuum manifold through which air is drawn. The vacuum manifolds draws in air through the perforations, which causes the sheets to remain on the belt, even as the belt moves at relatively high speeds. The belt is generally supported between two or more rollers (one or more of which can be driven) and are commonly used to transport sheets from a storage area (e.g., paper tray) or sheet cutting device (when utilizing webs of material) to a printing engine.

In addition, printers improve performance by detecting locations of the leading and trailing edges of the sheets of media. For example, this allows the printing engine to properly align printing on the sheet of media, and avoids applying marking materials (e.g., inks, toners, etc.) to the belt itself. Common sheet edge detection devices include optical sensors (e.g., laser sensors) or similar devices; however, such optical sensors can be expensive and difficult to align/focus, and they may not always detect the sheet edges properly, especially when there is little difference between the color, or appearance, of the sheet and the belt.

SUMMARY

Apparatuses herein include components of, or an entire, printing device; and such devices include (among other components) a printing engine, a sheet supply, a belt (such as a conductive vacuum belt) positioned to move sheets of media from the sheet supply to the printing engine, etc.

Further, such devices include electrically conductive elements (such as electrically conductive wheels, contacts, leads, arms, bars, etc.) contacting the belt. Additionally, these devices include a voltage source connected to the electrically conductive elements. The sheets of media contact the outer surface of the belt, and the electrically conductive elements contact the same outer surface of the belt. The electrically conductive elements are in a fixed position adjacent the belt, and the electrically conductive elements maintain contact with belt as the belt moves by the electrically conductive elements. Further, these electrically conductive elements are positioned so that they are separated from (temporarily disconnected from or insulated from) the belt by the sheets of media on the belt (e.g., when the belt moves the sheets of media between the electrically conductive elements and the belt).

Also, a voltage detector is operatively connected to the voltage source. The voltage source, the electrically conductive elements, the belt, and the voltage detector form an electrical circuit (potentially with a common ground connection). The voltage detector is capable of detecting the voltage of the electrical circuit.

Further, a processor is operatively connected to the voltage detector. The processor is capable of identifying leading edges of the sheets of media on the belt (when voltage of the electrical circuit changes from a relatively higher voltage to a relatively lower voltage) and identifying trailing edges of the sheets of media on the belt (when the voltage of the electrical circuit changes from the relatively lower voltage back to the relatively higher voltage). The relatively higher voltage can be, for example, at least two times the relatively lower voltage. Thus, the processor is capable of identifying positions of the sheets of media based on these leading and trailing edges.

These and other features are described in, or are apparent from, the following detailed description.

