Duplex Print Recovery Using Sheet Recirculation After Defect Ejection

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Solution Overview

Problem

Ink jet printers face issues with sheet defects causing collisions between sheets and print heads, leading to waste and contamination, especially in duplex printing, where semi-finished sheets are discarded due to the recovery time needed for print heads, resulting in significant waste production.

Innovation Solution

Recirculate subsequent semi-finished sheets in the duplex loop while interrupting the supply of fresh sheets, allowing duplex printing to resume after the print heads are ready, minimizing waste by keeping sheets in the loop until they can be correctly oriented for printing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If sheet defect detection and ejection is implemented upstream of the print engine, then print head damage and contamination are prevented, but semi-finished sheets in the duplex loop must be discarded to preserve page sequence

Engineering Contradiction:

Improveprint head protectionVSAvoidsheet waste

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The system performs preliminary detection of sheet defects upstream of the print engine using a sheet surface height scanner. When a defect is detected, the defective sheet is ejected before it can reach the print engine, preventing potential damage and contamination. This preliminary action allows the system to protect the print engine while maintaining the ability to continue printing with subsequent sheets.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of discarding semi-finished sheets when a defect is detected, the invention inverts the conventional approach by recirculating these sheets in the duplex loop. The system temporarily suspends the supply of fresh sheets and allows semi-finished sheets to complete their circulation and be printed on the second side, thereby preserving them rather than discarding them.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If print head recovery routine is performed after sheet defect error, then print head function is restored, but recirculation time exceeds interval between successive sheets requiring discarding of semi-finished sheets

Engineering Contradiction:

Improveprint head function restorationVSAvoidprint head recovery time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary detection and ejection of defective sheets before they reach the print engine, preventing the need for recovery routines. By detecting sheet surface height anomalies upstream and ejecting defective sheets in advance, the print engine never encounters conditions that would require time-consuming recovery operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention maintains continuous printing operation by recirculating semi-finished sheets in the duplex loop while temporarily suspending fresh sheet supply. This allows the printing process to continue without interruption on the recirculated sheets, eliminating idle time that would occur while waiting for print head recovery and ensuring continuous productive action.

Inventive Principle:

Principle #20Continuity of useful action

3Productivity

If large capacity duplex loop is used to maintain page sequence, then more sheets can be recirculated, but more fresh sheets must be discarded when recovery time exceeds sheet interval

Engineering Contradiction:

Improvesheet recirculation capacityVSAvoidfresh sheet waste

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

The system performs preliminary detection and ejection of defective sheets before they enter the duplex loop, preventing the need to discard recirculated sheets. By identifying and removing defective sheets upstream, the system ensures that only good sheets are recirculated and printed, eliminating waste of both fresh and recirculated sheets.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention inverts the conventional waste management approach by preserving recirculated sheets instead of discarding them. When a defect is detected, the system suspends fresh sheet supply and allows semi-finished sheets to complete their circulation and printing, thereby inverting the normal flow where fresh sheets are continuously supplied and defective ones discarded.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentEP3991977B1A method of handling a sheet defect error in a duplex print process

Publication Date: 2025.12.31 CANON PRODN PRINTING HLDG BV

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AI summary

A method of handling a sheet defect error in a duplex print process wherein media sheets (12, 14, 18) are successively supplied along a feed path (10) and are moved past a print engine (16) where a first image is printed on a first side of each sheet in a first print pass, the sheets are then returned, via a duplex loop (24) that contains a sheet flipping mechanism (26), to the feed path (10) upstream of the print engine (16) so that a second image can be printed on a second side of each sheet in a second print pass, the finished sheets (18) being then discharged in a predetermined page sequence, and wherein, when a sheet defect is found a first print pass of a sheet (s16), the defective sheet is diverted into an eject path (32) downstream of the print engine (16), and a print pass for an immediate successor (s3) of the defective sheet is skipped, characterized in that the subsequent semi-finished sheets (14) are recirculated in the duplex loop (24) while the supply of fresh sheets (12) into the feed path (10) is interrupted, and duplex printing is resumed during or after recirculating the subsequent semi-finished sheets (14).