Image Forming Apparatus DC Power Shutoff Mechanism

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Solution Overview

Problem

Conventional image forming apparatuses face difficulties in effectively suppressing the application of direct current (DC) voltage, which can lead to malfunctions and potential damage, such as thermostat welding, due to the risk of DC power being outputted during AC power source malfunctions.

Innovation Solution

An image forming apparatus is designed with a drive system powered by AC power, incorporating a detector to identify DC power input and a shutoff member that immediately shuts off the power supply to prevent DC voltage application, utilizing a mechanical switch and actuator mechanism to ensure safe operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a triac is used to block power supply when overvoltage is detected, then the power supply can be interrupted, but DC voltage application cannot be effectively suppressed

Engineering Contradiction:

Improvepower supply interruption capabilityVSAvoidDC voltage application

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The mechanical switch is positioned upstream in the power supply circuit to preemptively block DC voltage before it reaches the drive. The detector continuously monitors for DC voltage and triggers the mechanical switch to open before DC voltage can cause harmful effects, implementing a preliminary protective action rather than reactive protection.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A mechanical switch is introduced as an intermediary component between the power source and the drive. This mechanical intermediary physically interrupts the circuit when DC voltage is detected, providing a reliable barrier that prevents DC voltage from reaching sensitive components, unlike the triac which cannot effectively block DC.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Difficulty of detecting and measuring

If an overvoltage detection circuit is used, then voltage abnormalities can be detected, but DC power detection capability is insufficient

Engineering Contradiction:

Improvevoltage abnormality detectionVSAvoidDC power detection accuracy

Core Design Contradiction:

Difficulty of detecting and measuringVSMeasurement precision

Solution Approach 1:

The detection approach is changed from general overvoltage detection to specific DC voltage detection. The detector is designed to identify the unique characteristics of DC voltage (unidirectional current flow, absence of zero-crossing points) rather than merely detecting high voltage levels, enabling precise differentiation between AC overvoltage and DC voltage intrusion.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If a triac is used for power shutoff, then the circuit can be interrupted, but the shutoff mechanism is insufficient for DC voltage protection

Engineering Contradiction:

Improvepower shutoff functionVSAvoidDC voltage suppression reliability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent replaces the electronic triac-based shutoff mechanism with a mechanical switch system. The mechanical switch, actuated by a detector that identifies DC voltage, provides a physically robust circuit interruption capability that is inherently suitable for blocking DC current, unlike the triac which relies on semiconductor junctions that cannot effectively block DC.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS12164251B2Image forming apparatus

Publication Date: 2024.12.10 SHARP KK

AI summary

An image forming apparatus includes a drive that is driven by alternating current (AC) power; a detector that detects input of direct current (DC) power to the drive; and a shutoff member that shuts off power supply to the drive based on a detection result by the detector.