JP2004198914A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize a start-up operation adaptively to changes of conditions (heater characteristics, power source, installation environment, etc.) related to an individual device when a fixing heater is started up target temperature in its start-up operation while a rush current is deterred from being generated. <P>SOLUTION: Since voltage variation of a commercial power source can be detected with a zero-cross signal width, operation parameters (frequency of software start, turn-on phase value) of a software start at start-up time of the heater is varied with a difference in zero-cross signal width after the heater turn-on operation. Changes of the parameters are made to correspond to the difference; when the changes are large, the software start frequency is increased and a phase timer value is corrected in a direction where in the turn-on time is shortened. Each time a zero-cross signal is generated, a CPU is interrupted to change settings of the parameters, thereby optimizing the software start operation following up secular changes. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

上記［表１］において、
Ａ：サンプリングした最新のサーミスタ温度データ
Ｂ：（最新のサーミスタ温度データ）−（前回のサーミスタ温度データ）
Ｔ：設定目標温度
を表す。
ここに、上記［表１］は設定目標温度Ｔを１８０℃とした場合を示しており、ＯＮデューティとして示した数値は、以下の５パターンを用いている。それぞれの数値の意味は、次の通りである
１００：ソフトスタート処理を行い、サンプリング周期内で全点灯
７０：ソフトスタート処理を行い、周期内の７０％の時間を点灯させる
５０：ソフトスタート処理を行い、周期内の５０％の時間を点灯させる
３０：ソフトスタート処理を行い、周期内の３０％の時間を点灯させる
０：周期内でヒータは消灯
【００１５】
上記のようにしてＬＴＢ方式により検索した結果が0％以外だったら、位相角制御にてソフトスタートを実行し、位相角制御デューティが100％になったら、上記で決定された制御デューティに相当する時間定着ヒータをＯＮし続ける。
例えば、制御周期が１秒で制御デューティが50％の場合、ソフトスタート終了後に「0.5秒−ソフトスタート時間」の間定着ヒータをＯＮして、0.5秒間ＯＦＦする。
ソフトスタートは以下に記載の方法で、位相角制御デューティや回数を機器とその設置環境により増減する。
ソフトスタートのパラメータとして設定する位相角制御デューティ値は、例えば、30→40→50→100％と言うステップで変化させる。
また、ソフトスタート回数については、50Ｈｚの場合に例えば、3回×10ｍｓｅｃ＝30ｍｓｅｃ（コールドスタート時は30回×10ｍｓｅｃ＝0.3ｓｅｃ）という目安でソフトスタートを終了させる。
図６は、上記したソフトスタート動作を可能にするヒータ制御動作によるヒータの駆動結果を示す。図６に示す例は、制御周期が１秒で上記５パターンのＯＮデューティの制御デューティで動作され、30ｍｓｅｃ程度のソフトスタートをかけた（立ち上がりの傾斜により表す）場合を示している。
【００１６】
本発明では、ヒータ制御において装置条件や環境条件等の違いによりヒータ立ち上げ時の突入電流による電圧降下が変動しても、変動に対応して最適なソフトスタート動作を行うようにする。この動作は、装置条件や環境条件の違いにより変動する電源電圧の変動をゼロクロス信号幅の変化により検出し、検出値に応じてソフトスタートの動作パラメータの設定を変更することにより対応する。
この電源電圧の検出方法は、商用電源電圧の低下でゼロクロス信号幅が広くなり、商用電源電圧の上昇でゼロクロス信号幅が狭くなるという検出原理を用いたものである。例えば、定格電圧で1ｍｓｅｃ幅のゼロクロス信号が発生し、信号幅計測用の計数クロックを1ＭＨｚとした場合、およそ“1000”クロックのカウント値となる。
従って、クロックのカウント値に関連して次の認識を得る。
・「クロックのカウント値 大（上記の例で1000より大）」→「ゼロクロス幅＿大」→「電圧 降下、又は商用電源電圧 低下」
・「クロックのカウント値 小（上記の例で1000より小）」→「ゼロクロス幅＿小」→「電圧 降下無し、又は商用電源電圧 上昇」
【００１７】
次に、ゼロクロス信号幅の変化に追従して最適化されるソフトスタート制御の手順に係わる１実施形態を説明する。
本実施形態のソフトスタート制御は、画像形成動作時の定着ヒータ制御の一環として行うので、上記で説明したヒータ制御システム、即ちシステム制御板３０のＣＰＵが制御プログラムを実行することによりシステム制御板３０上に構築されるシステム、のシーケンスの一部として行われる。
ソフトスタート制御シーケンスの開始条件は、上記したように、定着ヒータ制御システムが定着装置(定着ローラ)１９の温度変化を検出し、点灯処理アルゴを行った結果、即ち検出した温度変化に基づいて、例示したようなＬＴＢ方式(上記表[１]のテーブル参照)によりＯＮデューティ値(点灯制御値)を検索した結果が０％以外だった場合に、位相角制御によるソフトスタートを実行する。
この実施形態におけるソフトスタート制御の手順では、ゼロクロス信号幅の変化に応じた動作を行うために、点灯前後におけるゼロクロス信号幅の検出値の差分をとり、差分に応じソフトスタートの動作パラメータの設定(初期設定)を変更(補正)し得るようにして、各装置に固有の条件に適合したソフトスタート動作を行わせるようにする。
また、初期設定を変更し、変更した動作パラメータに従い微小点灯（位相角制御によるソフトスタート時の点灯）を行った後、ソフトスタートの実行過程でゼロクロス信号幅のチェックをして、そのたびに動作パラメータの設定処理を繰り返すという手順を行うことにより、経時的な変動に追従してソフトスタート動作の最適化を図ることができるようにする。
さらに、検出したゼロクロス信号幅が異常値を示すときには、画像形成装置の稼動が出来ない電源事情の悪さや定着ヒータの部品不良が生じた場合が想定されるので、ヒータを消灯して、未然に装置のトラブルを回避するような手順を用意する。
【００１８】
図７は、本実施形態のソフトスタート制御の手順を示すフローチャートである。
図７に示すフローを参照して、本例のソフトスタート制御動作を説明する。ヒータ制御システムがソフトスタートの開始を判断すると、この制御シーケンスが起動し、先ず、商用電源から検出するゼロクロス信号によるＣＰＵ割り込みで、ヒータ点灯前のゼロクロス信号幅の平均値を算出する（Ｓ１０１）。平均値を求めるのは、異常値の影響を排除し、他の機器の影響や補正量の相対性を向上できるようにするためで、電源投入時のＣＰＵイニシャル状態やヒータ以外の負荷変動が少ない待機状態おいて、所定回数分のゼロクロス信号幅をあらわすクロックカウンタ値の平均値を使用しても、新しいデータに重みをつける重加算方式で求めても良い。なお、ゼロクロス信号幅は、上記したようにクロックのカウンタ値として得られる。
次に、ゼロクロス信号幅の平均値を算出した後のゼロクロス信号によるＣＰＵ割り込みで、ソフトスタートの動作パラメータの設定処理を行う（Ｓ１０２）。本例では、ソフトスタートの動作パラメータとして、ソフトスタート回数及び点灯実効値としての位相タイマ値(位相角制御値)を用いる。ソフトスタート回数は、商用電源の半波を単位としてソフトスタートの位相角制御をかける(図８参照)ときに、何回でソフトスタートを終了させるかを決める数値である。また、位相タイマ値は、ヒータの点灯時間を決める値で、ゼロクロス信号からの時間値として与える。
【００１９】
図８は、ソフトスタート時の点灯動作及び位相タイマ値（位相角に相当）を説明する図である。同図に示すように、位相タイマ値を大きくするとヒータのＯＮ時間が短くなり、位相タイマ値を小さくするとヒータのＯＮ時間が長く、即ち点灯実効値が大きくなる（つまり、実際のタイマ値は、位相タイマ:0＞位相タイマ:100となる）。ここでは、位相タイマ値を0（：ヒータ消灯）〜100（：半波全期間点灯）の間で5きざみのステップ値をとるようにしている。
このステップ（Ｓ１０２）では、これらの動作パラメータの設定処理を行う際に、これまでに設定していたパラメータを個々の装置に関連する条件に適合するような設定に変更(補正)する。そのために、ヒータ点灯後にゼロクロス信号幅を求め、求めたゼロクロス信号幅とヒータ点灯前に求めたゼロクロス信号幅の差分を算出し、算出した差分に応じて、これまでに設定していたパラメータを変更(補正)する。パラメータの変更は、基本的には算出した差分のレベルの大きさに対応させるように、レベルが大きければソフトスタート回数は増やし、また位相タイマ値は点灯時間を減らす方向に補正を行う(下記、表［２］，表［３］参照)。このような補正を行うことにより、個々の装置に関連する条件に適合した設定を行うことができる。なお、初期設定値としては突入電流の発生を抑制する点灯条件として予め定められた適当な値を設定する。
【００２０】
ソフトスタートの動作パラメータの設定処理の後、ソフトスタートの終了を意味する位相タイマ値の設定が“100”であるか、あるいは点灯動作の停止を意味する位相タイマ値の設定が“0”であるか否かを確認して(Ｓ１０３)、設定が“100”又は“0”である場合には、ソフトスタート制御のフローを抜ける。
設定が“100”又は“0”以外の場合には、設定に従って動作を実行して、個々の装置に関連する条件に適合したソフトスタート動作で突入電流を抑え、微少点灯から徐々に立ち上げるヒータ電源の供給を行う（Ｓ１０４）。
なお、このようにしてヒータ点灯動作を実行する際に、先の動作パラメータの設定処理（Ｓ１０２）において１回の設定処理で定めたソフトスタート回数及び位相タイマ値に従う動作を最終回まで実行して、動作を終了させても良いが、ここでは、ゼロクロス信号によるＣＰＵ割り込みによりＳ１０２→Ｓ１０３→Ｓ１０４をループ処理し、そのたびに設定を変更し得るようにして、経時的な変動に追従してソフトスタート動作の最適化を図るようにしている。
【００２１】
次いで、ソフトスタートの制御手順に必要となる動作パラメータの設定処理を以下に示す実施形態により詳細に説明する。
図９は、本実施形態の動作パラメータの設定処理手順を示すフローチャートである。図９に示すフローは、上記したソフトスタートの制御シーケンス(図７)のパラメータの設定処理ステップ（Ｓ１０２）に適用することが可能な手順を示すものである。
図９に示すフローを参照して、本例の動作パラメータの設定処理を説明する。商用電源から検出するゼロクロス信号によるＣＰＵ割り込みで、処理が始まり(Ｓ２０１-YES)、ヒータが未点灯である場合には(Ｓ２０２-YES)、動作パラメータの初期設定を行う（Ｓ２０３）。動作パラメータの初期設定値としては、突入電流の発生を抑制する点灯条件として予め定められた適当な値を用いるが、ここでは、ソフトスタート回数:10、位相タイマ:5を設定する。
次いで、ゼロクロス信号幅の検出値であるクロックカウンタ値を記憶する（Ｓ２０４）。この記憶値は、ヒータ点灯前のゼロクロス信号幅として、後に行うヒータ点灯後のゼロクロス信号幅との差分を算出するときに用いられる。なお、ここで行うクロックカウンタ値の記憶ステップは、上述のソフトスタート制御フロー(図７)において算出したヒータ点灯前の平均ゼロクロス信号幅（Ｓ１０１）を用いる場合には、省略しても良いし、このステップ（Ｓ２０４）で得た値を含めて平均化処理をして求めた値を用いるようにしても良い。また、平均ゼロクロス信号幅の算出（Ｓ１０１）を省略する場合には、必ずこのクロックカウンタ値の記憶ステップ（Ｓ２０４）を設ける。
動作パラメータの初期設定等を行う初回の処理を終えて、このフローを抜けると、初期設定に従いヒータが点灯される(図７、Ｓ１０４参照)。
【００２２】
この後、再びゼロクロス信号によるＣＰＵ割り込みで、本フローを再開するが、ヒータは点灯されたので(Ｓ２０２-NO)、ソフトスタート回数を減算（-１）する（Ｓ２１１）。
ここで、点灯後の現時点におけるゼロクロス信号幅（最新の電源電圧の状態を示す）のクロックカウンタ値を取得する（Ｓ２１２）。
次に、得たヒータ点灯開始後における最新のゼロクロス信号幅の値と点灯前のゼロクロス信号幅の値（初回もしくは平均値）との差分を算出し、算出した差分を差分のレベルを区分するために所定値と比較し、比較結果それぞれに対応した設定の変更を行う。ここでは、クロックカウンタ値の差分を,10,15,30,60,80の境界値としてそれぞれを区分し、差分が小さい場合は（Ｓ２２０）、ソフトスタート回数をさらに減算し、合わせて、位相タイマの値を加算（+5(+5％相当)或いは+10(+10％相当)）してヒータ駆動実効値を増加させる（Ｓ２２１，２２２）。これにより不必要なソフトスタート処理を早く終了し、位相制御により生じる電源高調波やノイズ成分を低減できる。他方、差分が所定以上の場合には（Ｓ２１４，２１６，２１８-NO）、ソフトスタート回数の減算を行わず、初期の減算(即ちＳ２１１で行う減算(-1))のみとするか、もしくは加算（+1）として初期の減算を相殺しソフトスタート処理の延長を図り、合わせて、位相タイマの値を変更せず同等のヒータ駆動実効値のままとするか（Ｓ２１７，２１９）、位相タイマの値を減算（-5(-5％相当)）してヒータ駆動実効値を減少させ（Ｓ２１５）。ソフトスタート処理を繰り返すかさらに抑制をかける処理とする。なお、ヒータの突入電流は、通電によりフィラメント温度が上昇していくため同一のヒータ駆動実効値でも低減していく。
【００２３】
この実施形態では、上記の処理をゼロクロス信号によるＣＰＵ割込毎に実行し、ソフトスタート回数が“０”又は位相タイマが50（50%）を越えた段階で位相制御でなく全波通電とする（位相タイマを100とする処理）。本フローにおける手順としては、上記した動作パラメータ(ソフトスタート回数及び位相タイマ値)の変更処理を終えた後、ソフトスタート回数が“0”に達したか否かをチェックし（Ｓ２２３）、達しない場合にはさらに位相タイマ値が50を越えたか否かをチェックし（Ｓ２２４）、越えない場合には、再び次のＣＰＵ割込でソフトスタートの設定処理を行う。他方、ソフトスタート回数が“0”に達した場合や、位相タイマ値が50を越えた場合には、位相タイマ値を100とする処理を行い、本フローを抜ける。
また、ヒータ点灯開始後の最新のゼロクロス信号幅の値と点灯前のゼロクロス信号幅の値との差分が著しく大きい場合は（Ｓ２１３-NO）、電源事情の不良もしくは機器の異常/故障と判断し、ヒータ通電処理を中止する。本フローの手順としては、位相タイマ値を0とする処理を行うことにより、ヒータ消灯の処理を行い（Ｓ２３１）、オペレータに対する警告表示等の報知を必要に応じて行い（Ｓ２３２）、処理を抜ける。
【００２４】
上記した実施形態では、画像形成動作時を対象にした場合の動作を例示したが、上記したクロックカウンタ値の差分（ヒータ点灯前後のゼロクロス信号幅の差を示す）に応じたソフトスタート回数や位相タイマの変更（補正）は、電源投入時や省エネ状態から立ち上げて点灯する場合（コールドスタート）と、画像形成動作時の場合とで異なる補正量とする方がより適切な動作が可能になる。
コールドスタート時点では、ヒータ突入電流が大きい傾向があり、画像形成装置のその他の負荷変動も少ないため、クロックカウンタ値の差分が大きくなるので、差分が大きくなる部分を対象として適正な変更（補正）ができるように、動作パラメータの設定変更処理をおこなうための手段を用意することが必要になる。
例えば、コールドスタート時には、下記［表２］に示すような設定変更条件を用いることにより期待する結果が得られる。なお下記［表３］に両方を対比できるように画像形成時に用いる設定変更条件の例を示す。［表３］は、上記図９のフロー図に示した設定変更条件に沿うものである。
【表２】

【表３】

【００２５】
【発明の効果】
（１） 請求項１の発明に対応する効果
ヒータ点灯前後に検出した交流電源のゼロクロス信号幅の差分を求め、求めた差分に応じてヒータ点灯開始時に設定されたソフトスタート条件（ソフトスタートの動作パラメータ）を変更可能としたことにより、装置の動作条件（ヒータ特性のような装置条件や電源、設置環境のような環境条件など）に違いがあっても、適切なソフトスタートが可能になる。
（２） 請求項２の発明に対応する効果
上記（１）の効果に加えて、ソフトスタート条件（ソフトスタートの動作パラメータ）によりヒータの点灯を開始し、電源の制御値が所定値に達するまで、ゼロクロス信号幅の差分の検出と、求めた差分に応じて設定されているソフトスタート条件の変更をするようにしたので、経時的な電源変動に追従して(例えば、電圧の最大値を捕捉し)ソフトスタートを最適化することが可能になる。
（３） 請求項３の発明に対応する効果
検出したゼロクロス信号幅の差分が所定値以上になったときにはヒータへの電力の供給を停止するようにしたので、安定した画像形成装置の稼動が出来ない電源事情の悪さや定着ヒータの部品不良が生じた場合にも、これらに起因して生じる可能性のある事故、故障を未然に防止することが可能になる。なお、電源事情には、例えば、商用電源においては、100V系といっても各国の仕様により100V，110V，115V，120V，125Vと異なる電源電圧が存在し、100〜110Vを100V系、115〜125Vを120V系として設計・搭載する場合が多いが、基本となる商用電源電圧の違いは定着ローラの加熱特性に影響を与えるレベルとなる場合もあり、こうした事情に対しても対応することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係わる複写機全体の構成を概略的に示す。
【図２】本発明の実施形態に係わる感光体装置、定着ユニット、電源制御回路の関係を示すブロック図である。
【図３】本発明の実施形態に係わる複写機の各部の動作を制御するシステムブロック図を示す。
【図４】定着ヒータの駆動制御に係わる回路ブロック図を示す。
【図５】定着ヒータの温度サンプリングを説明する図である。
【図６】ソフトスタートを伴う定着ヒータ制御動作の駆動状態を示す。
【図７】定着ヒータのソフトスタート制御手順を示すフローチャートである。
【図８】ソフトスタート時の点灯動作及び位相タイマ値を説明する図である。
【図９】ソフトスタート制御における動作パラメータの設定処理手順を示すフローチャートである。
【符号の説明】
１０…画像形成部、 １１…感光体、
１９…定着装置、 ３０…システム制御板、
３４…Ｉ／Ｏ制御板、 ４０…ＰＳＵ(電源ユニット)、
５０…定着サーミスタ、 ４３…ハロゲン(定着)ヒータ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for forming an image by an electrophotographic process (for example, a copying machine, a printer, a facsimile apparatus, and an apparatus combining these functions, etc.), and more specifically, to a target of a fixing unit used in an image forming process. The present invention relates to an image forming apparatus including a heater control unit that suppresses an inrush current to a heater that heats a fixing unit when the temperature rises to a temperature and performs a soft start.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, an electrostatic latent image is generated on the surface of a photoreceptor drum, toner (developer) is adhered to the latent image, developed by toner, and the toner image is further recorded on a recording paper. Image forming process (hereinafter, referred to as “electrophotographic process”) in which the transferred toner is fixed to recording paper by fusing and pressing.
In this electrophotographic process, a temperature condition required for stable fixing is obtained by using a heater (halogen heater) as a heat source provided in the fixing device. The heating by the fixing heater is stopped when the main power supply is not turned on or the standby (power saving: energy saving) mode is not performed, or the fixing device (fixing roller) is kept at a standby temperature (lower temperature). Is controlled as follows. Thereafter, when the main power supply is turned on or an instruction to cancel the standby mode is issued, the fixing heater is activated, or the heating operation of the heater is switched to start up until a standby (copyable) state is reached.
In recent years, in order to warm up the fixing device, one of the issues is to shorten the time from the viewpoints of improving power energy consumption efficiency and improving operability and convenience.
[0003]
In order to shorten the warm-up time, a fixing roller having a small heat capacity and a small thermal resistance and a halogen heater of high power or a halogen heater having a plurality (two) are often used.
However, in a high-power halogen heater, in the cold start state (for example, after the main power supply is turned off for a long time), an inrush current that greatly exceeds the rated current flows at the time of start-up, and the peripheral equipment drops due to a drop in the commercial power supply voltage. Therefore, it is required not to generate such a current.
Conventionally, as a method for suppressing such rush current to the heater, a method using a heater driving method is known. This is a method in which AC power for driving the heater is applied by phase angle control. In this method, the power starts from a small phase angle at startup and gradually increases until the power is finally applied over the entire phase angle. (The operation at the time of startup in which the power is gradually increased is referred to as “soft start”) so as to suppress the inrush current generated at the time of startup in a state where the resistance value of the cold start is low.
[0004]
[Problems to be solved by the invention]
However, in a method known so far in which a heater is soft-started by a method of applying an AC drive power supply by phase angle control, a method of performing an operation as set according to phase angle control data prepared in advance is used. Has been taken.
For this purpose, specific conditions relating to the device such as device conditions (conditions relating to the operating characteristics of the heater), power supply conditions of the device (conditions relating to a power supply for driving the heater), and installation environment of the device (for example, a cold region). In addition, when it is not possible to cope with the fluctuations of the above-mentioned conditions that change with time, it is not always possible to realize an appropriate soft start, that is, even if the inrush current becomes excessive or the inrush current can be suppressed, In some cases, the fixing device (fixing roller) cannot be heated to the target temperature by the time.
The present invention relates to an image forming apparatus having a fixing heater for heating a fixing apparatus used in an image forming process to a target temperature (for example, a copying machine, a printer, a facsimile apparatus, and an apparatus combining these functions). The purpose of the present invention is to suppress the occurrence of an inrush current that may occur when the fixing heater whose driving is stopped is started, and to start up to a target temperature. In addition, an appropriate start-up operation is performed in response to fluctuations in conditions (device conditions such as heater characteristics, power supply, environmental conditions such as installation environment, etc.) related to each device, It is an object of the present invention to provide an image forming apparatus including means for performing an optimum start-up operation while being able to cope with a temporary fluctuation.
[0005]
[Means for Solving the Problems]
The invention according to claim 1 includes a heater for heating a fixing unit used in an image forming process, a temperature detecting unit for the fixing unit, and the heater for heating the fixing unit to a target temperature in accordance with a detection value of the temperature detecting unit. What is claimed is: 1. An image forming apparatus comprising: a heater control unit for controlling an ON time of an AC power source to be turned on, wherein said heater control unit includes a unit for detecting a zero cross signal width of the AC power source; An image forming apparatus comprising: means for obtaining a difference in width and enabling a soft start condition set at the start of heater lighting to be changed according to the obtained difference.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the heater control means repeatedly detects the difference in the zero-cross signal width until the control value of the power supply based on the soft start condition reaches a predetermined value. Means for changing the soft start condition set according to the obtained difference.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the heater control unit supplies power to the heater when the difference between the detected zero-cross signal widths is equal to or greater than a predetermined value. It is characterized by stopping.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described based on the following embodiments shown in the accompanying drawings.
As an embodiment related to the image forming apparatus of the present invention, a copying machine that forms an image by an electrophotographic process will be exemplified here.
FIG. 1 schematically shows the configuration of the entire copying machine exemplified in the present embodiment. The copying machine shown in FIG. 1 is a general type device using a commercial power supply.
FIG. 1 shows an outline of an apparatus layout of basic components necessary for processing of reading a document and performing copy output based on read data in response to an operation performed by an operator requesting a copy. . In the figure, reference numeral 22 denotes a reading unit / operation unit. The operation unit includes keys, a display, and the like for an operator (user) to input setting conditions and a start operation in a dialog system. The reading unit includes a scanner device for reading a document placed on a contact glass or an automatic document feeder (ADF) as digitized data. An image forming unit 10 includes a processing element for forming an image by an electrophotographic process based on read data from a reading unit. The image forming unit 10 will be further described later with reference to FIG. Reference numeral 26 denotes a paper feed unit, which includes a paper feed tray and a mechanism for transporting the transfer paper loaded thereon to the image forming unit 10. Reference numeral 24 denotes a transfer paper stack unit which receives a copy discharged from the image forming unit 10 and deposits it until it is taken out.
[0007]
FIG. 2 schematically illustrates the configuration of the image forming unit in the copying machine according to the present embodiment. The image formation is performed by an electrophotographic process. As shown in FIG. 2, the OPC (photoconductor) 11 charged by the charging roller 12 is exposed by LD (laser diode) writing, and the generated latent image on the OPC 11 is The image is developed by the developing unit 15. The toner image formed after the development is transferred by a transfer roller 18 to a transfer sheet sent from a sheet feed roller 17 via a sheet conveyance path, and is thermally fixed by a fixing device 19 at a final stage.
When a toner cartridge configuration is employed, the cartridge is composed of the photoreceptor 11, the charging roller 12, and the developing unit (including the toner bottle 13, the toner agitator, and the like). In addition to the charging roller 12 facing the photoreceptor 11, the toner cartridge contains an agitator and a blade for stirring the toner, and the toner is charged by friction. A toner detecting means (sensor) 14 for detecting the presence / absence of toner inside the toner cartridge is disposed below the toner cartridge, and outputs “H” when there is toner and “L” when there is no toner.
The registration sensor 16 is located in front of a registration roller (not shown), and detects the leading end of the transfer sheet and the sheet state when the drive is performed in synchronization with the leading end of the image and the leading end of the transfer sheet.
[0008]
FIG. 3 is a block diagram of a system for controlling the operation of each unit in the copying machine according to the present embodiment.
The main operation of the reading control plate 31 is to generate a CCD for reading the document information in the reading section and its timing, and transfers the read output to the system control plate 30 as a digital signal.
The system control board 30 includes a CPU, a ROM, a RAM, a nonvolatile RAM, a calendar function chip, etc., and controls timing of the entire system, input / output control of the operation / display unit 32, and other application (FAX, printer, scanner, etc.) units. (Not shown) and control of the whole system such as operation control, image processing of image information data (magnification, filter, γ correction, etc.), storage / storage control of image information data using image memory Govern
The writing control board 33 is composed of an LD for exposing the photosensitive member and a driving unit thereof, and controls the light emission of the LD based on image data from the system control board 30 to perform a writing operation.
The I / O control board 34 is used for input signals of various sensors and actuators provided in various parts of the system such as a reading (scanner) section and an image forming (printer) section, and output signals of motors, solenoids, clutches, high voltage power supplies and the like. The output of the toner sensor 37 and the output of each thermistor are input to an ADC (Analog Digital Converter). The I / O data is used by the system control board 30 to drive a fixing heater, which will be described in detail below. The control of various drive systems including this is executed. The I / O data also includes various image forming I / Os 35 using a paper sensor for a paper feed tray and a manual feed tray, size information, a registration sensor for transferring a transfer sheet, and the like.
The operation / display unit 32 is constituted by a display unit using keys, LEDs, LCDs, 7 seg, etc., for the operator (user) to perform various mode setting input operations. ing.
[0009]
The fixing heater according to the main part of the present invention will be described.
FIG. 4 is a circuit block diagram related to driving control of the fixing heater.
A circuit for generating power and a circuit for driving the fixing halogen heater 43 are provided on the PSU (power supply unit) 40. The heater drive circuit includes a relay for cutting off AC power, a triac, a snubber circuit, and the like for turning ON / OFF the drive power to the heater at a specific cycle. The ON / OFF processing of the relay and the triac is executed via the port of the I / O control board 34 according to the judgment of the CPU on the system control board 30.
The ON / OFF timing of the triac employs a phase angle control method, and changes the effective value of the supply voltage to the heater by controlling the power supply according to the phase angle from the zero cross point of the commercial (AC) power supply voltage. enable. In addition to controlling the fixing device 19 to the target temperature during the normal image forming process by this method, in order to suppress the rush current at the time of starting the heater, the power is started from a small phase angle at the time of starting, and finally, the electric power is supplied over the entire phase angle. The power is increased stepwise until the voltage is applied, and the soft start control process is performed.
[0010]
Furthermore, in the soft start control, the control operation is optimized by checking the fluctuation of the commercial (AC) power supply voltage, and for this purpose, the commercial power supply voltage is detected. In the present embodiment, this detection method is based on a method using a characteristic in which the zero-cross signal width increases as the commercial power supply voltage decreases and the zero-cross signal width decreases as the commercial power supply voltage increases. For this reason, the zero-cross signal of the commercial power supply voltage is treated as a gate signal, and the signal width is generated by capturing the occurrence of the zero-cross signal with a clock counter of a high-frequency clock (system clock, CPU clock) or the like. It can be detected accurately. In the present embodiment, a zero-cross signal width is detected by asserting the zero-cross signal to generate a CPU interrupt, resetting / starting the clock counter, and negating the zero-cross signal to stop the clock counter. In general, a zero-cross signal is obtained by dividing a commercial power supply, performing full-wave rectification by a diode bridge, connecting the waveform to a light emitting unit of a photocoupler, and forming an ON / OFF signal (L / H signal). .
[0011]
When the image forming apparatus is left in the power saving state for a long time or when the power is turned off, the temperature of the fixing roller becomes about room temperature, and the fixing heater is turned on by returning from the power saving state or turning on the power. The temperature of the (fixing roller) is increased (starting up from a so-called cold start state). At that time, an inrush current (generally, a value such as 10 times or more of the rated current) is generated at the start of energization to the fixing heater.
The rush current is reduced by continuing the energization, but often reaches a level exceeding the rated current for 5 to 15 cycles with a commercial power supply. The power supply impedance rises due to the inrush current during this time, and the image forming apparatus and peripheral devices fall into a voltage drop due to the impedance rise.
In this case, the level of the voltage drop depends on device conditions such as variation in components (for example, an increase or decrease in the number of W of the fixing heater), a power source, and an installation environment (a commercial environment where the outside temperature is lower than the general environment). It greatly differs depending on environmental conditions such as a low power supply voltage), and in the related art which does not consider such device-specific conditions, inrush current cannot be prevented.
Therefore, the present invention enables a soft-start operation that suppresses an inrush current in response to fluctuations in device conditions, environmental conditions, and the like, and enables an optimal soft-start operation in response to temporal fluctuations in the above conditions. Is performed.
[0012]
Next, a description will be given of heater control that enables an optimal soft start operation in response to fluctuations in device conditions, environmental conditions, and the like. The system for performing the heater control is constructed on the system control board 30, and the control operation is realized by the CPU of the system control board 30 executing the control program.
The control method of the fixing heater will be described focusing on the operation during the image forming operation.
There is provided a means for sampling a heater temperature detected by a fixing thermistor 39 provided in the fixing device (thermal fixing roller) 19, and the sampling means samples the heater temperature at predetermined intervals. The heater control system receives the sampled detected temperature as the newest data signal, calculates a change from the immediately preceding data signal that has already been received, and calculates a change from the newest data signal and the change data signal. In accordance with one data signal or a second data signal including the newest data signal and the immediately preceding data signal, heater drive data is selected from a data table previously input to the heater control system. Then, the power supply to the heater is turned on and off according to the selected data, and if there is a sign of a temperature decrease from the target temperature, the heater temperature is kept high, and if there is a sign of a temperature rise, the heater temperature is kept low. Thus, the level of the heat fixing roller surface temperature from a predetermined target value and the thermal ripple are minimized.
[0013]
The heater control based on the above-described basic control operation can be performed in the following example.
In this embodiment, as shown in FIG. 5, the detection of the heater temperature is performed at a predetermined sampling cycle. In the figure, the sampling periods a, b, c, で are constant, and the data D1, D2, D3, そ れ ぞ れ are respectively detected as sampling temperature data at sampling time points t1, t2, t3, ‥‥‥. I do.
The latest sampled data is referred to as “latest thermistor temperature data”, and the data sampled immediately before that is referred to as “previous thermistor temperature data”. That is, in FIG. 5, in the section of the sampling period b, the sampling data D2 at the sampling time t2 is defined as “the latest thermistor temperature data”, and the sampling data D1 at the sampling time t1 is defined as “the previous thermistor temperature data”. The ON duty of the fixing heater is determined based on the two data D2 and D1 thus obtained. Thereafter, the ON duty is determined in accordance with the sampling cycle by a similar process performed using “latest thermistor temperature data” and “last thermistor temperature data”.
[0014]
As a means for determining the ON duty from the latest thermistor temperature data and the previous thermistor temperature data (or the temperature change), a table is created in which ON duty values determined in advance by a combination of the two temperature data are created. It is possible to use the LTB method of searching for a control value from a table during operation.
One example of this table is shown in [Table 1] below. In the table shown in this example, a combination obtained from two changes between the latest temperature data and the previous temperature data is represented by a 5 * 5 matrix.
[Table 1]

In the above [Table 1],
A: Latest sampled thermistor temperature data
B: (Latest thermistor temperature data)-(Previous thermistor temperature data)
T: Set target temperature
Represents
Here, [Table 1] shows a case where the set target temperature T is set to 180 ° C., and the numerical value shown as the ON duty uses the following five patterns. The meaning of each value is as follows
100: Performs soft start processing and lights up all within the sampling cycle
70: Perform soft start processing and turn on 70% of the period
50: Perform soft start processing and turn on 50% of the period
30: Performs soft start processing and turns on 30% of the period
0: The heater is turned off within the cycle
[0015]
If the result searched by the LTB method as described above is other than 0%, the soft start is executed by the phase angle control, and when the phase angle control duty becomes 100%, it corresponds to the control duty determined above. The fixing heater is kept ON for a certain time.
For example, when the control cycle is 1 second and the control duty is 50%, the fixing heater is turned on for "0.5 seconds-soft start time" after the soft start ends, and is turned off for 0.5 seconds.
In the soft start, the phase angle control duty and the number of times are increased or decreased according to the device and its installation environment by the method described below.
The phase angle control duty value set as a parameter of the soft start is changed in steps of, for example, 30 → 40 → 50 → 100%.
As for the number of times of soft start, in the case of 50 Hz, for example, the soft start is terminated on the basis of 3 times × 10 msec = 30 msec (30 times × 10 msec = 0.3 sec at cold start).
FIG. 6 shows a heater driving result by the heater control operation enabling the above-described soft start operation. The example shown in FIG. 6 shows a case where the control cycle is 1 second, the operation is performed with the above-described five patterns of the ON duty control duty, and a soft start of about 30 msec is applied (represented by a rising slope).
[0016]
According to the present invention, even if the voltage drop due to the rush current at the time of starting the heater fluctuates due to a difference in apparatus conditions, environmental conditions, and the like in the heater control, an optimal soft start operation is performed in response to the fluctuation. This operation is performed by detecting a change in the power supply voltage that fluctuates due to a difference in device conditions or environmental conditions from a change in the zero-cross signal width, and changing the setting of the soft start operation parameter according to the detected value.
This method of detecting the power supply voltage uses a detection principle that the zero-cross signal width increases as the commercial power supply voltage decreases, and the zero-cross signal width decreases as the commercial power supply voltage increases. For example, when a zero-cross signal of 1 msec width is generated at the rated voltage and the counting clock for measuring the signal width is 1 MHz, the count value is approximately "1000" clocks.
Therefore, the following recognition is obtained in relation to the clock count value.
・ "Clock count value is large (greater than 1000 in the above example)" → "Zero cross width_large" → "Voltage drop or commercial power supply voltage drop"
・ "Clock count value small (less than 1000 in the above example)" → "Zero cross width_Small" → "No voltage drop or commercial power supply voltage rise"
[0017]
Next, a description will be given of an embodiment relating to a procedure of a soft start control which is optimized according to a change in a zero cross signal width.
Since the soft start control according to the present embodiment is performed as a part of the fixing heater control during the image forming operation, the above-described heater control system, that is, the CPU of the system control board 30 executes the control program to execute the control program. This is done as part of the sequence of the system built above.
As described above, the start condition of the soft start control sequence is based on the result of the fixing heater control system detecting the temperature change of the fixing device (fixing roller) 19 and performing the lighting process algo, that is, based on the detected temperature change. If the result of searching for the ON duty value (lighting control value) by the LTB method as illustrated (see the table in Table [1] above) is not 0%, the soft start by the phase angle control is executed.
In the procedure of the soft start control in this embodiment, in order to perform an operation according to the change of the zero cross signal width, a difference between the detected values of the zero cross signal width before and after the lighting is taken, and setting of the soft start operation parameter according to the difference ( (Initial setting) can be changed (corrected) so that each device performs a soft start operation suited to the unique conditions.
In addition, after changing the initial setting, perform minute lighting (lighting at soft start by phase angle control) according to the changed operation parameter, check the zero cross signal width in the process of executing soft start, and operate each time By performing the procedure of repeating the parameter setting processing, it is possible to optimize the soft start operation by following a temporal change.
Furthermore, when the detected zero-cross signal width indicates an abnormal value, it is assumed that the power supply condition that the image forming apparatus cannot operate or a defective component of the fixing heater may occur. Prepare procedures to avoid equipment trouble.
[0018]
FIG. 7 is a flowchart illustrating a procedure of the soft start control according to the present embodiment.
The soft start control operation of the present example will be described with reference to the flow shown in FIG. When the heater control system determines the start of the soft start, the control sequence is started, and first, an average value of the zero cross signal width before the heater is turned on is calculated by a CPU interrupt by a zero cross signal detected from a commercial power supply (S101). The purpose of calculating the average value is to eliminate the influence of the abnormal value and to improve the influence of other devices and the relativity of the correction amount, so that the CPU initial state at power-on and load fluctuations other than the heater are small. In the standby state, the average value of the clock counter value representing the zero-cross signal width for a predetermined number of times may be used, or the average value may be obtained by a multiple addition method that weights new data. The zero-cross signal width is obtained as a clock counter value as described above.
Next, a process of setting an operation parameter for soft start is performed by a CPU interrupt due to a zero-cross signal after calculating an average value of the zero-cross signal width (S102). In this example, the number of soft starts and the phase timer value (phase angle control value) as the lighting effective value are used as the operation parameters of the soft start. The number of soft starts is a numerical value that determines how many times the soft start is to be ended when controlling the phase angle of the soft start in units of half-waves of the commercial power supply (see FIG. 8). Further, the phase timer value is a value that determines the lighting time of the heater, and is given as a time value from the zero cross signal.
[0019]
FIG. 8 is a diagram illustrating a lighting operation and a phase timer value (corresponding to a phase angle) at the time of soft start. As shown in the figure, when the phase timer value is increased, the ON time of the heater is shortened, and when the phase timer value is decreased, the ON time of the heater is extended, that is, the lighting effective value is increased (that is, the actual timer value is (Phase timer: 0> phase timer: 100). Here, the phase timer value is set to a step value in increments of 5 between 0 (: heater off) to 100 (: full-wave full-time lighting).
In this step (S102), when performing the setting processing of these operation parameters, the parameters that have been set so far are changed (corrected) to settings that match the conditions related to each device. For this purpose, the zero-cross signal width is calculated after the heater is turned on, the difference between the calculated zero-cross signal width and the zero-cross signal width obtained before the heater is turned on is calculated, and the parameters that have been set are changed according to the calculated difference. (to correct. The parameter change is basically made to correspond to the calculated level of the difference, so that if the level is large, the number of soft starts is increased, and the phase timer value is corrected to decrease the lighting time (see below, See Tables [2] and [3]). By performing such a correction, it is possible to perform settings suitable for the conditions relating to each device. In addition, as the initial setting value, an appropriate value predetermined as a lighting condition for suppressing the occurrence of the rush current is set.
[0020]
After the setting process of the soft start operation parameter, the setting of the phase timer value indicating the end of the soft start is “100” or the setting of the phase timer value indicating the stop of the lighting operation is “0”. It is determined whether or not the setting is “S” (S103). If the setting is “100” or “0”, the flow exits the soft start control flow.
When the setting is other than "100" or "0", the heater is executed according to the setting, the inrush current is suppressed by the soft start operation suitable for the conditions related to each device, and the heater is gradually started from the minute lighting. Power is supplied (S104).
When the heater lighting operation is performed in this manner, the operation according to the number of soft start times and the phase timer value determined in one setting process in the previous operation parameter setting process (S102) is executed until the last time. , The operation may be terminated, but here, the CPU interrupts by a zero-cross signal to perform a loop processing of S102 → S103 → S104, so that the setting can be changed each time, and the software can follow the temporal change. The start operation is optimized.
[0021]
Next, a process of setting operation parameters required for a soft start control procedure will be described in detail with reference to the following embodiments.
FIG. 9 is a flowchart illustrating a procedure for setting operation parameters according to the present embodiment. The flow shown in FIG. 9 shows a procedure that can be applied to the parameter setting processing step (S102) of the above-described soft start control sequence (FIG. 7).
With reference to the flow shown in FIG. 9, the operation parameter setting processing of the present example will be described. The process starts with a CPU interrupt by a zero-cross signal detected from the commercial power supply (S201-YES). If the heater is not turned on (S202-YES), the operation parameters are initialized (S203). As the initial setting value of the operation parameter, an appropriate value predetermined as a lighting condition for suppressing occurrence of an inrush current is used. Here, the number of soft starts: 10, and the phase timer: 5, are set.
Next, a clock counter value which is a detected value of the zero cross signal width is stored (S204). This stored value is used when calculating the difference between the zero-cross signal width before the heater is turned on and the zero-cross signal width after the heater is turned on. Note that the clock counter value storage step performed here may be omitted when the average zero-cross signal width before heater lighting (S101) calculated in the above-described soft start control flow (FIG. 7) is used. A value obtained by performing an averaging process including the value obtained in this step (S204) may be used. When the calculation of the average zero-cross signal width (S101) is omitted, a step of storing the clock counter value (S204) is always provided.
When the process exits from this flow after the initial processing for initial setting of operation parameters and the like, the heater is turned on according to the initial setting (see S104 in FIG. 7).
[0022]
Thereafter, this flow is restarted by the CPU interrupt by the zero cross signal again, but since the heater is turned on (S202-NO), the number of soft starts is subtracted (−1) (S211).
Here, the clock counter value of the zero-cross signal width (indicating the latest power supply voltage state) at the present time after lighting is acquired (S212).
Next, the difference between the latest value of the zero-cross signal width after the start of heating of the heater and the value of the zero-cross signal width before the lighting (first time or average value) is calculated, and the calculated difference is classified into a difference level. Then, the setting is compared with the predetermined value, and the setting corresponding to each comparison result is changed. Here, the difference between the clock counter values is classified as a boundary value between 10, 15, 30, 60, and 80. If the difference is small (S220), the number of soft starts is further reduced, and the phase timer is added. Are added (+5 (corresponding to + 5%) or +10 (corresponding to + 10%)) to increase the heater drive effective value (S221, 222). As a result, unnecessary soft-start processing can be completed early, and power supply harmonics and noise components generated by phase control can be reduced. On the other hand, when the difference is equal to or more than the predetermined value (S214, 216, 218-NO), the subtraction of the number of soft starts is not performed, and only the initial subtraction (that is, the subtraction (-1) performed in S211) is performed or added. (+1), the initial subtraction is canceled to extend the soft start process. In addition, the same effective heater drive value is maintained without changing the value of the phase timer (S217, 219). The value is subtracted (-5 (equivalent to -5%)) to decrease the heater drive effective value (S215). It is assumed that the soft start process is repeated or further suppressed. Note that the inrush current of the heater is reduced even with the same heater drive effective value because the filament temperature is increased by energization.
[0023]
In this embodiment, the above-described processing is executed for each CPU interrupt by the zero-cross signal, and when the number of soft starts is “0” or the phase timer exceeds 50 (50%), full-wave energization is performed instead of phase control. (Process for setting the phase timer to 100). As a procedure in this flow, after finishing the above-described change processing of the operation parameters (the number of soft starts and the phase timer value), it is checked whether or not the number of soft starts has reached “0” (S223). In this case, it is further checked whether or not the phase timer value has exceeded 50 (S224). If not, the soft start setting process is performed again at the next CPU interrupt. On the other hand, if the number of soft starts has reached “0” or if the phase timer value has exceeded 50, a process for setting the phase timer value to 100 is performed, and the flow exits.
If the difference between the latest value of the zero-cross signal width after the start of heating of the heater and the value of the zero-cross signal width before the lighting is extremely large (S213-NO), it is determined that the power supply is defective or the equipment is abnormal / failed. Then, the heater energizing process is stopped. As a procedure of this flow, a process of turning off the heater is performed by performing a process of setting the phase timer value to 0 (S231), and a warning display or the like to the operator is performed as needed (S232), and the process exits. .
[0024]
In the above-described embodiment, the operation when the image forming operation is performed has been described as an example. However, the number of times of the soft start and the phase corresponding to the difference of the clock counter value (indicating the difference of the zero cross signal width before and after the heater is turned on) are described. When changing (correcting) the timer, it is more appropriate to use a different correction amount between when the power is turned on or when the power is turned on after starting up from the energy saving state (cold start) and when the image forming operation is performed. .
At the time of the cold start, the inrush current of the heater tends to be large, and other load fluctuations of the image forming apparatus are small, so that the difference between the clock counter values becomes large. Therefore, an appropriate change (correction) is performed for a portion where the difference becomes large. Therefore, it is necessary to provide a means for performing a process of changing the setting of the operation parameter so that the operation can be performed.
For example, at the time of a cold start, an expected result can be obtained by using a setting change condition as shown in the following [Table 2]. Table 3 below shows examples of setting change conditions used during image formation so that both can be compared. [Table 3] is in accordance with the setting change conditions shown in the flowchart of FIG.
[Table 2]

[Table 3]

[0025]
【The invention's effect】
(1) Effects corresponding to the first aspect of the invention
The difference between the zero-cross signal widths of the AC power supply detected before and after the heater is turned on is determined, and the soft start condition (soft start operation parameter) set at the start of the heater lighting can be changed according to the obtained difference. Even if there are differences in operating conditions (device conditions such as heater characteristics, power supply, environmental conditions such as installation environment, etc.), appropriate soft start can be performed.
(2) Effects corresponding to the second aspect of the invention
In addition to the effect of the above (1), the lighting of the heater is started under the soft start condition (the operation parameter of the soft start), and the difference of the zero cross signal width is detected and obtained until the control value of the power supply reaches a predetermined value. The soft start condition set according to the difference is changed, so that it is possible to optimize the soft start by following the power supply fluctuation over time (for example, by capturing the maximum value of the voltage). Become.
(3) Effects corresponding to the invention of claim 3
When the difference between the detected zero-cross signal widths becomes equal to or greater than a predetermined value, the supply of power to the heater is stopped, so that a poor power supply condition in which stable operation of the image forming apparatus cannot be performed and a defective component of the fixing heater are caused. Even if it occurs, it is possible to prevent accidents and failures that may occur due to them. In the power supply situation, for example, in the case of a commercial power supply, there are power supply voltages different from 100 V, 110 V, 115 V, 120 V, and 125 V depending on the specifications of each country even if it is 100 V system. In many cases, 125V is designed and mounted as a 120V system, but the difference in the basic commercial power supply voltage may affect the heating characteristics of the fixing roller in some cases. .
[Brief description of the drawings]
FIG. 1 schematically shows a configuration of an entire copying machine according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a relationship between a photoconductor device, a fixing unit, and a power supply control circuit according to the embodiment of the present invention.
FIG. 3 is a system block diagram for controlling the operation of each unit of the copying machine according to the embodiment of the present invention.
FIG. 4 is a circuit block diagram related to driving control of a fixing heater.
FIG. 5 is a diagram illustrating temperature sampling of a fixing heater.
FIG. 6 shows a driving state of a fixing heater control operation with a soft start.
FIG. 7 is a flowchart illustrating a soft start control procedure of the fixing heater.
FIG. 8 is a diagram illustrating a lighting operation and a phase timer value at the time of soft start.
FIG. 9 is a flowchart showing a procedure for setting operation parameters in soft start control.
[Explanation of symbols]
10 image forming unit 11 photoconductor
19: fixing device, 30: system control board,
34 ... I / O control board, 40 ... PSU (power supply unit),
50: fixing thermistor, 43: halogen (fixing) heater.

Claims (3)

A heater for heating the fixing unit used in the image forming process, a temperature detecting unit of the fixing unit, and an ON time of an AC power supply for lighting the heater according to a detection value of the temperature detecting unit for heating the fixing unit to a target temperature. An image forming apparatus having a heater control means for controlling the AC power supply, wherein the heater control means has a means for detecting a zero-cross signal width of the AC power supply, and obtains a difference between the zero-cross signal widths detected before and after the heater is turned on. An image forming apparatus comprising: means for changing a soft start condition set at the start of heater lighting according to the difference. 2. The image forming apparatus according to claim 1, wherein the heater control unit repeats the detection of the difference in the zero-cross signal width until the control value of the power supply under the soft start condition reaches a predetermined value, and according to the obtained difference. An image forming apparatus comprising means for changing a set soft start condition. 3. The image forming apparatus according to claim 1, wherein the heater control unit stops supplying power to the heater when the difference between the detected zero-cross signal widths is equal to or greater than a predetermined value. Image forming device.

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