Image Forming Apparatus Over Stacking Detection via Conveyance Time

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Solution Overview

Problem

Conventional image forming apparatuses face challenges in accurately detecting over stacking of sheets, particularly with envelope type sheets, due to air accumulation and pressure-induced errors, leading to feeding failures and inaccurate height measurements.

Innovation Solution

The apparatus employs a time-counting unit to measure the conveyance time of sheets and determines over stacking based on a threshold value, rather than relying solely on height sensors, to accurately detect and prevent feeding failures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If height sensor is used to detect over stacking, then over stacking detection is provided, but detection accuracy deteriorates with envelope type sheets due to air accumulation and pressing down

Engineering Contradiction:

Improveover stacking detection reliabilityVSAvoidheight measurement precision

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the detection parameter from height (which is affected by air accumulation in envelopes) to conveyance time. By measuring how long it takes for sheets to be conveyed through the system, the invention achieves accurate over-stacking detection without being influenced by the compressibility of envelope materials.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If locking claw is used to regulate sheet number, then sheet stacking is controlled, but feeding failure occurs when large number of envelope sheets are forcibly over-stacked

Engineering Contradiction:

Improvesheet stacking controlVSAvoidfeeding reliability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent performs preliminary detection of over-stacking conditions by measuring conveyance time before feeding failures occur. By detecting abnormal conveyance time that indicates over-stacking, the system can prevent feeding failures from happening in the first place, rather than just responding after the locking claw causes problems.

Inventive Principle:

Principle #10Preliminary action

3Extent of automation

If sensor-based height detection is used, then over stacking detection is enabled, but detection accuracy is insufficient for envelope type sheets

Engineering Contradiction:

Improveautomatic over stacking detectionVSAvoidover stacking detection precision

Core Design Contradiction:

Extent of automationVSMeasurement precision

Solution Approach 1:

The patent replaces the mechanical height sensor-based detection system with a time-based detection system. Instead of physically measuring the height of the sheet stack with a sensor, the system uses timing measurements of sheet conveyance to infer stacking conditions, achieving higher precision especially for envelope materials.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9802778B2Image forming apparatus for forming image on sheet

Publication Date: 2017.10.31 CANON KK

AI summary

An image forming apparatus may comprise the following elements. A stacking unit in which a sheet is stacked. A conveyance unit conveys the sheet. A time-counting unit counts a conveyance time from when the conveyance unit starts to convey the sheet until the sheet arrives at a predetermined position on a conveyance path. A determination unit determines that over stacking has occurred, if the conveyance time of the sheet exceeds a first over stacking threshold value.