JP2004195926A - Control unit for electric injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control unit for an electric injection molding machine that makes a synchronized position control by torque control with a multi-shaft servo motor without using a mechanical belt. <P>SOLUTION: The control unit is constituted of a convertor 22 which calculates a first command on the amount of movement of the screw based on the command on injection speed, a pressure controller 28 which calculates a second command on the amount of movement of the screw based on the difference between a commanded injection pressure and an actual injection pressure, a comparator 30 which compares the first command on the amount of movement of the screw and the second command on the amount of movement of the screw and selects smaller one as the final command on the amount of movement of the screw and a plurality of servo amplifiers 40a and 40b which drive and control a plurality of the motors based on the selected final command on the amount of movement of the screw. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

ここで、Ｋ_Ｐｖは速度制御器４９の比例ゲインであり、Ｔ_Ｉｖは速度制御器４９の積分時間である。
【００３６】
なお、サーボアンプ４０ａ内では、位置制御ループのマイナループとして速度制御ループが形成されている。
【００３７】
速度制御器４９からの出力であるモータ電流指令ｉ_ｖと圧力制御器２８からの出力であるモータ電流指令ｉ_ｐとが入力される比較器４３は、ｉ^＊ _ｖとｉ^＊ _ｐの小さいほうの値を選択し、その値を最終的なモータ電流指令ｉ^＊としてＰＷＭ回路５０に入力する。ＰＷＭ回路５０は与えられたモータ電流指令ｉ^＊に基づいて所定の３相電圧をサーボモータ３ａに印加する。これにより、サーボモータ３ａはモータ電流ｉ^＊で駆動する。
【００３８】
また、比較器４３は位置制御ループにより決定されるモータ電流指令ｉ^＊ _ｖを制御ループ外からのモータ電流指令ｉ^＊ _ｐによって制限するために設けられている。
【００３９】
次に、この比較器４３の動作により前述した２つの要求課題が実現されることを、図４を用いて説明する。
まず、図４の充填工程の終了時間であるｔ_１が、実際にキャビティ１２に樹脂が十分充填される時間よりも前に設定されていた場合を考える。このときは、キャビティ１２内にはまだ空隙が存在するので射出圧力は一般的に低くなっている。この状態から次の保圧工程に入るときには、一般に射出圧力指令Ｐ^＊ _ｉのほうが実際の射出圧力よりも高いので、実際の射出圧力を高くするために圧力制御器２８から出力されるモータ電流指令ｉ^＊ _ｐが大きくなる。
【００４０】
ここで、モータ電流指令ｉ^＊ _ｐが最終的なモータ電流指令として採用されたとすると、キャビティ１２内が未充填なので射出速度が上昇する。これにより、図４（ｂ）の射出速度指令を上回ってしまうおそれがある。
【００４１】
しかし、比較器４３では常にｉ^＊ _ｖとｉ^＊ _ｐのうちで小さいほうの値が選択されるので、充填中に保圧制御に移行してｉ^＊ _ｐがｉ^＊ _ｖを上回っても、比較器４３においてｉ^＊ _ｖが最終的なモータ電流指令として採用される。
【００４２】
つまり、射出圧力制御から射出速度制限に移行させることができ、前述の要求課題（２）を常に満足させることが可能である。
【００４３】
次に、図４の充填工程の終了時間であるｔ_１が、実際にキャビティ１２に樹脂が十分充填される時間よりも後に設定されていた場合を考える。このときはキャビティ１２内に樹脂が十分充填されていても、まだ充填工程中であるので射出速度制御を実行する。しかし、この時点ではキャビティ１２が十分充填されているので実際のスクリュ速度はかなり低下している。そのため、速度制御器４９から出力されるモータ電流指令ｉ^＊ _ｖが大きくなる。
【００４４】
ここで、モータ電流ｉ^＊ _ｖが最終的なモータ電流指令として採用されたとすると、既にキャビティ１２内に樹脂が十分充填されているので急激に射出圧力が上昇する。これにより、図４（ｃ）の射出圧力指令を上回ってしまうおそれがある。
【００４５】
しかし、比較器４３では常にｉ^＊ _ｖとｉ^＊ _ｐのうちで小さいほうの値が選択されるので、充填が完了し、ｉ^＊ _ｖがｉ^＊ _ｐを上回っても、比較器４３においてｉ^＊ _ｐが最終的なモータ電流指令として採用される。
【００４６】
つまり、射出速度制御から射出圧力制限に移行させることができ、前述の要求課題（１）を常に満足させることが可能である。
【００４７】
【特許文献１】
特許第２６５２２７４号公報
【００４８】
【特許文献２】
特許第２６５２２７５号公報
【００４９】
【特許文献３】
特開平４−３１４８８号公報
【００５０】
【特許文献４】
特許第２９９２３２９号公報
【００５１】
【特許文献５】
特許第２７４６４７４号公報
【００５２】
【特許文献６】
特許第２６２８７７０号公報
【００５３】
【特許文献７】
特許第２６２８７６９号公報
【００５４】
【非特許文献１】
稲葉善治,上口賢男,根子哲明,電動式射出成形機における圧力波形追従制御（第１報）−流動圧力制御における学習制御の適用,“精密工学会誌”,65,2,(1999),pp.293-299
【００５５】
【非特許文献２】
稲葉善治,上口賢男,根子哲明,電動式射出成形機における圧力制御,“精密工学会誌”,65,4,(1999),pp.542-548
【００５６】
【非特許文献３】
稲葉善治,上口賢男,根子哲明,電動式射出成形機における圧力波形追従制御（第２報）−圧力波形編集制御における学習制御の適用,“精密工学会誌”,65,5,(1999),pp.746-752
【００５７】
【発明が解決しようとする課題】
図５において、２台のサーボモータ３ａ，３ｂのそれぞれのサーボアンプ４０ａ，４０ｂには、射出速度指令Ｖ^＊ _ｉに対しては共通の速度指令用パルス列が与えられる。しかし、射出圧力指令Ｐ^＊ _ｉに対しては、圧力検出センサ１０ａがアナログ信号を出力するので、結果としてサーボアンプ４０ａ，４０ｂには、共通のアナログ電流指令ｉ^＊ _ｐが与えられることになる。
【００５８】
したがって、比較器４３が、両サーボモータ３ａ，３ｂに与えるモータ電流指令ｉ^＊としてｉ^＊ _ｖを選択したときには、両ボールねじのナット７ａ，７ｂの移動量は図５の位置制御ループにより同じ量になることが保証される。このため、可動部８が両側のボールねじ５ａ，５ｂから不当な回転モーメントを受けることはない。
【００５９】
しかし、比較器４３が両サーボモータ３ａ，３ｂに与えるモータ電流指令ｉ^＊としてｉ^＊ _ｐを選択したときには、例え両サーボモータ３ａ，３ｂに同じモータ電流指令ｉ^＊ _ｐが与えられたとしても、両ボールねじのナット７ａ，７ｂの移動量が図５の位置制御ループから開放されているので、両ボールねじ５ａ，５ｂの負荷分担の相異などにより同じ量になることは保証されない。このため、可動部８が両側のボールねじ５ａ，５ｂから不当な回転モーメントを受けることがある。可動部８は前述したように、一般に２本のレール上を摺動移動するリニアガイドで保持される構造になっているので、不当な回転モーメントはリニアガイドに過度の横応力を発生させ、結果としてレールの破損などを生じさせる。
【００６０】
つまり、図５のような構造による２軸駆動制御では、射出速度制御に関してはモータエンコーダ１１ａからのフィードバック信号を用いることができるので２軸共通の位置指令パルス信号を使用しての２軸位置同期制御を行うことが可能である。しかし、射出圧力制御を行うトルク制御ではフィードバック信号がロードセル信号であるので２軸位置同期制御を行うことが困難であり、レールの破損などが生じてしまう可能性がある。
【００６１】
このレールの破損などを防止するために、現状では、２台のモータ出力軸を歯付ベルトで機械的に結合して位置同期制御を実現するマスタスレーブ方式を採用している。このマスタスレーブ方式は、マスタとなるサーボモータが速度制御又はトルク制御され、スレーブとなるもう一方のモータはマスタモータの実電流を電流指令として受ける方式である。しかし、このようなマスタスレーブ方式では、機械ベルトを用いることにより機械が大型化しやすく、また機械ベルトの保守なども行う必要もある。
【００６２】
本発明は、上記の事情に鑑みてなされたもので、機械ベルトを用いずに、多軸サーボモータによるトルク制御での位置同期制御が可能である電動射出成形機の制御装置を提供することを目的とする。
【００６３】
【課題を解決するための手段】
上記の目的を達成するために、本発明による電動射出成形機の制御装置は、第１のスクリュ移動量指令を算出する第１のスクリュ移動量指令算出手段と、上記第１のスクリュ移動量指令とは異なる第２のスクリュ移動量指令を算出する第２のスクリュ移動量指令算出手段と、上記第１のスクリュ移動量指令と上記第２のスクリュ移動量指令とを比較して、何れか小さいほうを最終的なスクリュ移動量指令として選択する比較手段とを含む射出制御部と、上記比較手段によって選択された最終的なスクリュ移動量指令に基づいて出力する比較手段とを含む射出制御部とを具備することを特徴とする。
【００６４】
また、上記の目的を達成するために、本発明による電動射出成形機の制御装置は、複数のサーボモータと、この複数のサーボモータの回転によって回転駆動される複数のボールねじと、この複数のボールねじの回転によりボールねじの回転軸方向に移動する複数のナットと、この複数のナットの移動により駆動される可動部と一体で構成されたスクリュとから構成される電動射出成形機を制御する電動射出装置の制御装置において、射出速度指令を出力する射出速度シーケンスと、この射出速度シーケンスから出力される射出速度指令に基づいて所定の制御演算時間間隔の間に上記スクリュが移動すべき量を第１のスクリュ移動量指令として算出する変換器と、射出圧力指令を出力する射出圧力シーケンスと、射出圧力を検出する射出圧力検出センサと、この射出圧力検出センサからの射出圧力検出結果を受けるＡ／Ｄ変換器と、上記射出圧力指令と上記Ａ／Ｄ変換器を介して入力された射出圧力検出結果とから射出圧力制御偏差を算出する第１の減算器と、上記第１の減算器で算出された射出圧力制御偏差に基づいて所定の制御演算時間間隔の間に上記スクリュが移動すべき量を第２のスクリュ移動量指令として算出する圧力制御器と、上記第１のスクリュ移動量指令と上記第２のスクリュ移動量指令とを比較して、何れか小さいほうの値を最終的なスクリュ移動量指令として出力する比較器と、この比較器から出力された上記最終的なスクリュ移動量指令に相当する数のパルスを上記制御演算時間間隔で速度指令パルス列として発生させるパルス発生器とを含む射出制御器と、上記パルス発生器からの速度指令パルス列のパルス数を計数して該計数したパルス数に相当する信号を位置指令として出力する第１のカウンタと、モータの実位置を検出する第２のカウンタと、上記第１のカウンタ及び第２のカウンタの出力から位置制御偏差を算出する第２の減算器と、上記第２の減算器で算出された位置制御偏差に基づいて上記複数のサーボモータの位置制御を行う位置制御ループとを含む上記複数のサーボモータと同数のサーボアンプとを具備することを特徴とする。
【００６５】
【発明の実施の形態】
以下、本発明の実施の形態を図面を参照して説明する。
図１は、本発明の一実施の形態に係る電動射出成形機の制御装置の内部構成を示すブロック図である。
つまり、本一実施の形態の制御装置も射出制御器２０と複数のサーボアンプ４０ａ，４０ｂを含んで構成される。なお、射出制御器２０は特許請求の範囲に記載の「射出制御部」に対応する。また、サーボアンプ４０ａ，４０ｂは特許請求の範囲に記載の「モータ制御部」に対応する。
【００６６】
まず、射出制御器２０について説明する。射出制御器２０は一定時間Δｔ毎に制御演算を行い、制御指令を更新する。
【００６７】
つまり、本一実施形態の射出制御器２０は、射出速度指令タイムシーケンス２１、変換器２２、パルス発生器２３、アナログ／デジタル（Ａ／Ｄ）変換器２５、射出圧力指令タイムシーケンス２６、減算器２７、圧力制御器２８、比較器３０を含んで構成される。また、射出制御器２０には、圧力検出センサ１０ａが接続される。
【００６８】
ここで、変換器２２は特許請求の範囲に記載の「第１のスクリュ移動量指令算出手段」に対応する。また、圧力制御器２８は特許請求の範囲に記載の「第２のスクリュ移動量指令算出手段」に対応し、比較器３０は特許請求の範囲に記載の「比較手段」に対応する。更に、射出速度指令タイムシーケンス２１は特許請求の範囲に記載の「射出速度指令手段」に対応し、射出圧力指令タイムシーケンス２６は特許請求の範囲に記載の「射出圧力指令手段」に対応する。
【００６９】
つまり、本一実施形態においては、前述の比較器４３に相当する機能をサーボアンプ側でなく射出制御器側に設けたところが大きな特徴である。これに伴って圧力制御器２８における演算が前述の図５の例と異なっているが、この演算については後に詳述する。
【００７０】
次にこのような射出制御器２０の動作について説明する。射出速度指令タイムシーケンス２１からの射出速度指令Ｖ^＊ _ｉに対して、変換器２２はΔｔ時間にスクリュ９が移動すべき量をスクリュ移動量指令Δｘ^＊ _ｖとして次の（式５）より算出する。
Δｘ^＊ _ｖ＝Ｖ^＊ _ｉΔｔ （式５）
そして、変換器２２は算出したスクリュ移動量指令Δｘ^＊ _ｖを比較器３０に入力する。
【００７１】
また、圧力検出センサ１０ａで検出された圧力を射出圧力センサ信号Ｐ_ｉとしてＡ／Ｄ変換器２５を介して射出制御器２０に取り込む。Ａ／Ｄ変換器２５は取り込んだ射出圧力センサ信号Ｐ_ｉを減算器２７に入力する。
【００７２】
ここで、圧力検出センサ１０ｂがもう一方のモータ駆動軸に取り付けられている場合には、２つの圧力検出センサ１０ａ，１０ｂの出力信号の平均値を射出圧力センサ信号Ｐ_ｉとする。
【００７３】
また射出圧力指令タイムシーケンス２６は、そのシーケンスに従った射出圧力指令Ｐ^＊ _ｉを減算器２７に入力する。減算器２７は射出圧力指令Ｐ^＊ _ｉと射出圧力センサ信号Ｐ_ｉとの制御偏差ΔＰ_ｉを次の（式６）により算出する。
ΔＰ_ｉ＝Ｐ^＊ _ｉ−Ｐ_ｉ （式６）
この後、算出した制御偏差ΔＰ_ｉを圧力制御器２８に入力する。
【００７４】
圧力制御器２８は、制御偏差ΔＰ_ｉに対してＰＩＤ制御演算を実行してモータΔｔ時間の間にスクリュ９が進むべき量をスクリュ移動量指令Δｘ^＊ _ｐとして算出する。そして、圧力制御器２８は算出したスクリュ移動量指令Δｘ^＊ _ｐを比較器３０に入力する。
【００７５】
比較器３０は２つのスクリュ移動量指令Δｘ^＊ _ｖとΔｘ^＊ _ｐのうちで小さいほうの値を次の（式７）により決定する。
Δｘ^＊＝ｍｉｎ（Δｘ^＊ _ｖ，Δｘ^＊ _ｐ） （式７）
ここで、この（式７）により前述の比較器４３に相当する機能、つまり、前述の要求課題（１）及び前述の要求課題（２）を満足させることができることを以下に説明する。
【００７６】
前述の（式５）により射出速度指令Ｖ^＊ _ｉは次の（式８）により表すことができる。
【数２】

【００７７】
このとき、圧力制御器２８の出力であるスクリュ移動量指令Δｘ^＊ _ｐを時間間隔Δｔで割れば、射出圧力制御に必要なスクリュ速度指令Ｖ^＊ _ｐが次の（式９）により得られる。
【数３】

【００７８】
また、（式７）の両辺を時間間隔Δｔで割れば、（式８）、（式９）により次の（式１０）が得られる。
【数４】

【００７９】
ここで、比較器３０が出力するスクリュ速度指令をＶ^＊とすれば、次の（式１１）が成り立つ。
【数５】

【００８０】
つまり、（式１０）、（式１１）により比較器３０の機能は次の（式１２）の演算を行うものであるとも考えることができる。
Ｖ^＊＝ｍｉｎ（Ｖ^＊ _ｉ，Ｖ^＊ _ｐ） （式１２）
射出開始当初は、金型１のキャビティ１２内に樹脂が充填されていないので射出圧力が低い。このため、射出開始時の高い射出圧力設定値に対して射出圧力制御偏差ΔＰ_ｉが大きくなる。したがって、圧力制御器２８の出力であるスクリュ移動指令Δｘ^＊ _ｐ、言い換えるとＶ^＊ _ｐが大きくなる。このため一般に、Ｖ^＊ _ｉ＜Ｖ^＊ _ｐとなる。このとき、比較器３０は（式１２）より、最終的なスクリュ速度指令Ｖ^＊としてＶ^＊ _ｉを選択し、Ｖ^＊＝Ｖ^＊ _ｉとなる。このことは（式７）の演算においてスクリュ移動量指令Δｘ^＊ _ｖが選択されたことを意味する。したがって、射出開始時は射出速度制御が優先されることになる。
【００８１】
また、射出速度制御中に射出圧力が上昇してΔＰ_ｉが小さくなると、圧力制御器２８の出力であるスクリュ移動量指令Δｘ^＊ _ｐ、言い換えるとΔＶ^＊ _ｐが小さくなる。つまり、Ｖ^＊ _ｉ＞Ｖ^＊ _ｐとなると、このとき比較器３０は（式１２）より、最終的なスクリュ速度指令Ｖ^＊としてＶ^＊ _ｐを選択し、Ｖ^＊＝Ｖ^＊ _ｐとなる。このことは（式７）の演算においてスクリュ移動量指令Δｘ^＊ _ｐが選択されたことを意味する。
【００８２】
したがって、射出速度制御から射出圧力制限に移行できるような制御、つまり、前述の要求課題（１）を満足させる制御を行うことができる。
【００８３】
また、射出圧力制御中に射出速度指令Ｖ^＊ _ｉが仮に小さくなった場合には、Ｖ^＊ _ｉ＜Ｖ^＊ _ｐとなる。このとき比較器３０は（式１２）より、最終的なスクリュ速度指令Ｖ^＊としてＶ^＊ _ｐを選択し、Ｖ^＊＝Ｖ^＊ _ｉとなる。
【００８４】
したがって、射出圧力制御から射出速度制限に移行できるような制御、つまり、前述の要求課題（２）を満足させる制御を行うことができる。
【００８５】
ここで、再び図１の説明に戻る。
比較器３０は、（式７）により最終的なスクリュ移動量指令Δｘ^＊を選択し、その後、このΔｘ^＊をパルス発生器２３に入力する。パルス発生器２３はΔｘ^＊に相当するモータエンコーダのパルス数をΔｔ時間内に速度指令用のパルス列２４として発生させ、各サーボアンプ内のカウンタ４１に入力する。
【００８６】
次にサーボアンプについて説明する。すなわち、サーボアンプ４０ａはカウンタ４１及び４４、減算器４５及び４８、位置制御器４６、微分回路４７、速度制御器４９、パルス幅変調制御（ＰＷＭ）回路５０を含んで構成される。また、このサーボアンプ４０ａは前述のサーボモータ３ａに接続されている。更にサーボモータ３ａにはモータエンコーダ１１ａが取り付けられている。
【００８７】
ここで、射出制御器２０に比較器３０を設けているので、図１のサーボアンプ内には比較器４３に相当するものが必要ない。
【００８８】
射出制御器２０からの速度指令用のパルス列２４を受けるサーボアンプ４０ａ内のカウンタ４１は、このパルス列のパルス数を計数して、スクリュ９の位置指令ｘ^＊を検出する。そして、このｘ^＊を減算器４５に入力する。
【００８９】
また、カウンタ４４はモータエンコーダ１１ａからのパルスを受ける。カウンタ４４はこのパルス数を計数して、スクリュ９の実際の位置ｘを検出する。そして、このｘを減算器４５に入力する。
【００９０】
減算器４５は入力されたｘ^＊及びｘから位置制御偏差（ｘ^＊−ｘ）を算出した後、この結果を位置制御器４６に入力する。位置制御器４６は次式より速度指令ｖ^＊を算出する。
ｖ^＊＝Ｋ_Ｐ（ｘ^＊−ｘ） （式１３）
ここで、Ｋ_Ｐは位置制御器４６の比例ゲインである。
【００９１】
なお、モータエンコーダ１１ａはパルスを、カウンタ４４の他に微分回路４７にも入力する。微分回路４７はこのパルスにより実速度ｖを検出する。そして、このｖを減算器４８に入力する。
【００９２】
減算器４８は入力されたｖ^＊及びｖから速度制御偏差（ｖ^＊−ｖ）を算出して速度制御器４９に入力する。速度制御器４９は次式によりモータ電流指令ｉ^＊を算出し、ＰＷＭ回路５０に入力する。
【数６】

ここで、Ｋ_Ｐｖは速度制御器４９の比例ゲインであり、Ｔ_Ｉｖは速度制御器４９の積分時間である。
【００９３】
ＰＷＭ回路５０は与えられたモータ電流指令ｉ^＊に基づいて所定の３相電圧をサーボモータ３ａに印加する。これにより、サーボモータ３ａはモータ電流ｉ^＊で駆動する。
【００９４】
以上説明したように、本一実施の形態によれば、射出制御器２０内のパルス発生器２３から２台のサーボモータ３ａ，３ｂのそれぞれのサーボアンプ４０ａ，４０ｂ内のカウンタ４１に同じパルス列が与えられ、更に、常に位置制御ループによる位置制御が行われるので、２台のサーボモータ３ａ，３ｂは同期のとれた回転角、すなわち、２台のサーボモータで駆動される２軸のボールねじ５ａ，５ｂの同期のとれた同じナット移動量を、射出速度制御中はもちろん、射出圧力制御中にも常に実現することが可能である。
【００９５】
これにより、機械ベルトを用いることなしに、射出圧力制御時に発生する２軸駆動の同期ずれによる構造強度上の問題を回避できる。
【００９６】
以上一実施の形態に基づいて本発明を説明したが、本発明は前述した一実施の形態に限定されるものではなく、本発明の要旨の範囲内で種々の変形や応用が可能なことは勿論である。例えば、前述の一実施の形態ではサーボモータを２台用いているがこれに限るものではない。また、本発明は電動射出成形機の射出・保圧機構にのみ限定して用いられるものではなく、可塑化機構、型開閉機構にも適用することが可能である。
【００９７】
【発明の効果】
以上詳述したように、本発明によれば、機械ベルトを用いずに、多軸サーボモータによるトルク制御での位置同期制御が可能である射出成形機の制御装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る電動射出成形機の制御装置の内部構成を示すブロック図である。
【図２】電動射出成形機における２軸駆動での射出・保圧機構の模式図である。
【図３】電動射出成形機の制御装置の概略図である。
【図４】電動射出成形機の制御装置の動作を説明するためのタイミングチャートである。
【図５】従来例による電動射出成形機の制御装置の内部構成を示すブロック図である。
【符号の説明】
１…金型、２…射出シリンダ、３ａ，３ｂ…サーボモータ、４ａ，４ｂ…減速機、５ａ，５ｂ…ボールネジ、６ａ，６ｂ…軸受、７ａ，７ｂ…ナット、８…可動部、９…スクリュ、１０ａ，１０ｂ…圧力検出センサ、１１ａ，１１ｂ…モータエンコーダ、１２…キャビティ、２０…射出制御器、２１…射出速度指令タイムシーケンス、２２…変換器、２３…パルス発生器、２５，４２…アナログ／デジタル（Ａ／Ｄ）変換器、２６…射出圧力指令タイムシーケンス、２７，４５，４８…減算器、２８…圧力制御器、２９…デジタル／アナログ（Ｄ／Ａ）変換器、３０，４３…比較器、４０ａ，４０ｂ…サーボアンプ、４１，４４…カウンタ、４６…位置制御器、４７…微分回路、４９…速度制御器、５０…パルス幅変調制御（ＰＷＭ）回路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an injection control device for controlling an injection speed and an injection pressure of an electric injection molding machine.
[0002]
[Prior art]
AC servo motors, which are characterized by high-precision control and excellent responsiveness, are increasing their capacity by improving the performance of permanent magnets used in the motors and reducing costs. As a result, AC servo drive using an AC servo motor has been rapidly applied to a medium-sized injection molding machine (a mold clamping force of 350 t to 1000 t) which was conventionally driven by hydraulic pressure. The advantages of using the AC servo drive in this injection molding machine are mainly that the molding stability can be improved, that there is an energy saving effect of about 50% by eliminating relief loss by hydraulic drive, There are three things.
[0003]
In addition, such an injection molding machine includes a plasticizing mechanism that melts resin pellets by rotating a screw, an injection / holding mechanism that injects a molten resin into a mold at a high speed by advancing the screw and holds the resin at a high pressure, and a metal mold. There is a mold opening and closing mechanism that opens and closes the mold. The AC servo drive can be applied to an injection molding machine having any of these mechanisms. Here, an AC servo control technique using an injection / pressure holding mechanism, which has many technical issues regarding the AC servo drive, will be described below.
[0004]
In an injection molding machine using an injection / holding mechanism, injection is generally performed as fast as possible in order to keep the temperature of a resin charged in a mold constant. However, if excessive injection pressure is generated due to excessively high speed, it may cause molding failure, so that the injection pressure is restricted to a predetermined value or less. Then, following such a step, there is a holding pressure step of applying pressure to the resin filled in the mold.
[0005]
These two steps are performed by an injection and pressure holding mechanism. Therefore, in the AC servo control in the injection and pressure holding mechanism, control in which speed control and torque (force) control are mixed is required.
[0006]
On the other hand, although the capacity of the servomotor has been increased, multi-axis driving of the servomotor is inevitable from the viewpoint of mechanical cost in order to achieve high-speed filling of resin. Currently, multi-axis driving of a servomotor is generally performed by two-axis driving using a combination of a servomotor and a ball screw.
[0007]
FIG. 2 is a schematic diagram of an injection / pressure-holding mechanism of an electric injection molding machine that operates by such a two-axis drive of a servomotor.
[0008]
The injection molding machine is provided with a moving device base (not shown) movable by a linear guide on an injection molding machine base (not shown) fixed on the ground. Further, all parts other than the mold 1 shown in FIG.
[0009]
By moving the moving device base, the tip of the injection cylinder 2 can be pressed against the mold 1, and conversely, the tip of the injection cylinder 2 can be separated from the mold 1. FIG. 2 shows a state in which the tip of the injection cylinder 2 is pressed against the mold 1 in order to inject the resin into the mold 1.
[0010]
A pair of servo motors 3a, 3b, reduction gears 4a, 4b, ball screws 5a, 5b, and bearings 6a, 6b are fixedly mounted on the moving device stand with their axes shown by dashed lines in the figure symmetrical. . Further, the nuts 7a and 7b, the movable portion 8, the screw 9, and the pressure detection sensors 10a and 10b of the ball screw have an integral structure. The movable portion 8 is mounted on a linear guide (not shown) so that the integrated structure can be moved back and forth by moving the nuts of the ball screws 5a and 5b.
[0011]
In such an injection molding machine, a pair of servomotors 3a and 3b are used for biaxial drive. This is to reduce the cost of the injection molding machine by using two small motors as described above. The rotational motion of the servo motors 3a, 3b is transmitted to ball screws 5a, 5b as a boosting mechanism via reduction gears 4a, 4b. Then, the rotational motion of the ball screws 5a, 5b is converted into a linear motion of the nuts 7a, 7b on the ball screw shaft. Thereby, the back-and-forth movement of the screw 9 via the movable part 8 is realized.
[0012]
The position of the screw 9 is detected by motor encoders 11a and 11b provided on the respective servo motor shafts. Further, the pressure applied by the screw 9 to the molten resin at the tip of the injection cylinder 2 is determined by a pressure detection sensor (for example, a load cell) 10 a, which is installed between the nuts 7 a and 7 b of the ball screw and the movable part 8. 10b.
[0013]
In such an injection molding machine driven by two axes, in order to prevent an excessive stress load from being applied to the machine body, synchronous control of the positions of the nuts 7a and 7b of the two ball screws, in other words, the positions of the two servomotors 3a and 3b are performed. Synchronous control is essential.
[0014]
Here, the injection step of making a molded article by the injection molding machine includes a filling step and a pressure-holding step. In the filling step, it is necessary to fill the cavity 12 with the molten resin in a short time. In the pressure-holding step after filling, it is necessary to apply pressure for a certain time until the molten resin is cooled.
[0015]
FIG. 3 schematically shows a control device of such an injection molding machine. That is, in this control device, the inputs are an injection speed command for instructing the injection speed, an injection pressure command for instructing the injection pressure, a motor encoder signal for detecting the position of the screw 9, and the actual injection. An injection pressure sensor signal for detecting pressure is provided. These inputs are processed in the control device, and finally a motor current command for commanding a motor current for controlling the driving of the motor is output.
[0016]
Generally, the following two requirements are given to the injection speed and injection pressure during the injection process.
[0017]
(1) During the filling process, a predetermined injection speed is realized, and at the same time, an injection pressure is equal to or lower than a predetermined pressure.
(2) During the pressure holding step, the injection speed is not higher than the predetermined speed while realizing the predetermined pressure.
[0018]
That is, during the filling step shown in FIG.₁4), injection speed control is performed so as to faithfully execute an injection speed command given as shown in FIG. 4B in order to realize a predetermined injection speed. However, the injection pressure must be controlled to be lower than the injection pressure command given as shown in FIG. Here, 100% shown on the vertical axis in FIGS. 4B and 4C indicates the maximum values of the injection speed and the injection pressure, respectively.
[0019]
Next, the pressure holding step (time t₁~ T₂4), injection pressure control is performed so as to faithfully execute an injection pressure command given as shown in FIG. 4C in order to realize a predetermined injection pressure. However, the injection speed must be controlled to be lower than the injection speed command given as shown in FIG.
[0020]
FIG. 5 is a block diagram for explaining the internal configuration of such a control device. This control device includes an injection controller 20 and servo amplifiers 40a and 40b.
[0021]
First, the injection controller 20 will be described. The injection controller 20 performs control calculation at regular time intervals Δt, and updates the control command.
[0022]
That is, the injection controller 20 includes an injection speed command time sequence 21, a converter 22, a pulse generator 23, an analog / digital (A / D) converter 25, an injection pressure command time sequence 26, a subtractor 27, and a pressure controller. And a digital / analog (D / A) converter 29. Further, the above-described pressure detection sensor 10a is connected to the injection controller 20.
[0023]
The injection speed command time sequence 21 includes an injection speed command V according to the sequence.^* _iIs output to the converter 22. The converter 22 receives the input injection speed command V^* _iIs the screw moving amount command Δx^* _vIs calculated by the following (Equation 1).
Δx^* _v= ΔV^* _iΔt (Equation 1)
Thereafter, the calculated screw movement amount command Δx^* _vIs output to the pulse generator 23.
[0024]
The pulse generator 23 outputs the screw movement amount command Δx^* _vGenerates a pulse train 24 including a number of pulses corresponding to. Then, the generated pulse train 24 is output to the counter 41 in the servo amplifiers 40a and 40b.
[0025]
Further, the pressure detected by the pressure detection sensor 10a is used as an injection pressure sensor signal P._iIs taken into the injection controller 20 via the A / D converter 25. The A / D converter 25 receives the injection pressure sensor signal P_iIs input to the subtractor 27.
[0026]
Here, when the pressure detection sensor 10b is attached to the other motor drive shaft, the average value of the output signals of the two pressure detection sensors 10a and 10b is used as the injection pressure sensor signal P_iAnd
[0027]
Further, the injection pressure command time sequence 26 includes an injection pressure command P according to the sequence.^* _iIs input to the subtractor 27. The subtractor 27 sets the injection pressure command P^* _iAnd injection pressure sensor signal P_iControl deviation ΔP_iIs calculated by the following (Equation 2).
ΔP_i= P^* _i-P_i                                  (Equation 2)
Thereafter, the calculated control deviation ΔP_iIs input to the pressure controller 28.
[0028]
The pressure controller 28 determines the control deviation ΔP_iPerforms a proportional-integral-derivative (PID) control operation on the motor current command i^* _pIs calculated. Then, the calculated motor current command i^* _pIs input to the servo amplifiers 40a and 40b via the D / A converter 29. In the servo amplifier 40a, the built-in A / D converter 42 controls the motor current command I^* _pAfter the motor current command I^* _pIs input to the comparator 43.
[0029]
Next, the servo amplifiers 40a and 40b will be described. Here, the servo amplifiers 40a and 40b are provided for driving the motor in two axes. Since the structures and operations of these servo amplifiers are the same, the following description will be made only for the servo amplifier 40a.
[0030]
That is, the servo amplifier 40a includes the counters 41 and 44, the A / D converter 42, the comparator 43, the subtractors 45 and 48, the position controller 46, the differentiating circuit 47, the speed controller 49, and the pulse width modulation control (PWM) circuit. 50. The servo amplifier 40a is connected to the servo motor 3a. Further, a motor encoder 11a is attached to the servo motor 3a.
[0031]
The counter 41 in the servo amplifier 40a which receives the pulse train 24 for the speed command from the injection controller 20 counts the number of pulses of the pulse train 24 and obtains the position command x of the screw 9.^*Is detected. And this x^*Is input to the subtractor 45.
[0032]
The counter 44 receives a pulse from the motor encoder 11a. The counter 44 counts the number of pulses to detect the actual position x of the screw 9. Then, this x is input to the subtractor 45.
[0033]
The subtractor 45 receives the input x^*And the position control deviation (x^*After calculating −x), the result is input to the position controller 46. The position controller 46 calculates the speed command v according to the following equation.^*Is calculated, and the result is input to the subtractor 48.
v^*= K_P(X^*−x) (Equation 3)
Where K_PIs a proportional gain of the position controller 46.
[0034]
Note that the motor encoder 11a inputs the pulse to the differentiation circuit 47 in addition to the counter 44. The differentiating circuit 47 detects the actual speed v from this pulse. Then, this v is input to the subtractor 48.
[0035]
The subtractor 48 receives the input v^*Speed control deviation (v^*-V) is calculated and input to the speed controller 49. The speed controller 49 calculates the motor current command i by the following equation.^* _vIs calculated and input to the comparator 43.
(Equation 1)

Where K_PvIs a proportional gain of the speed controller 49, and T_IvIs the integration time of the speed controller 49.
[0036]
In the servo amplifier 40a, a speed control loop is formed as a minor position control loop.
[0037]
Motor current command i, which is the output from speed controller 49_vAnd the motor current command i which is the output from the pressure controller 28_pIs input to the comparator 43.^* _vAnd i^* _pOf the motor current command i^*Is input to the PWM circuit 50. The PWM circuit 50 receives the given motor current command i^*, A predetermined three-phase voltage is applied to the servo motor 3a. As a result, the servo motor 3a receives the motor current i^*Drive with
[0038]
Further, the comparator 43 outputs a motor current command i determined by the position control loop.^* _vIs the motor current command i from outside the control loop.^* _pProvided to limit by.
[0039]
Next, how the above-described two required tasks are realized by the operation of the comparator 43 will be described with reference to FIG.
First, t, which is the end time of the filling step in FIG.₁However, a case where the time is set before the time when the resin is actually sufficiently filled in the cavity 12 is considered. At this time, the injection pressure is generally low because there is still a gap in the cavity 12. When entering the next pressure-holding step from this state, generally, the injection pressure command P^* _iIs higher than the actual injection pressure, the motor current command i output from the pressure controller 28 in order to increase the actual injection pressure.^* _pBecomes larger.
[0040]
Here, the motor current command i^* _pIs adopted as the final motor current command, the injection speed increases because the cavity 12 is not filled. As a result, the injection speed command shown in FIG. 4B may be exceeded.
[0041]
However, the comparator 43 always outputs i^* _vAnd i^* _pSince the smaller value is selected from among the values, the process shifts to the pressure-holding control during filling, and i^* _pIs i^* _vIs exceeded in the comparator 43.^* _vIs adopted as the final motor current command.
[0042]
That is, it is possible to shift from the injection pressure control to the injection speed limitation, and it is possible to always satisfy the above-mentioned required problem (2).
[0043]
Next, t, which is the end time of the filling step in FIG.₁However, it is assumed that the time is set after the time when the cavity 12 is filled with the resin sufficiently. At this time, even if the cavity 12 is sufficiently filled with resin, the injection speed control is executed because the filling process is still in progress. However, at this point, the actual screw speed is considerably reduced because the cavity 12 is sufficiently filled. Therefore, the motor current command i output from the speed controller 49^* _vBecomes larger.
[0044]
Here, the motor current i^* _vIs adopted as the final motor current command, the injection pressure rises rapidly because the cavity 12 is already sufficiently filled with resin. As a result, the injection pressure command shown in FIG. 4C may be exceeded.
[0045]
However, the comparator 43 always outputs i^* _vAnd i^* _pIs selected, the filling is completed and i^* _vIs i^* _pIs exceeded in the comparator 43.^* _pIs adopted as the final motor current command.
[0046]
That is, it is possible to shift from the injection speed control to the injection pressure limitation, and it is possible to always satisfy the above-mentioned required subject (1).
[0047]
[Patent Document 1]
Japanese Patent No. 2652274
[0048]
[Patent Document 2]
Japanese Patent No. 2652275
[0049]
[Patent Document 3]
JP-A-4-31488
[0050]
[Patent Document 4]
Japanese Patent No. 2992329
[0051]
[Patent Document 5]
Japanese Patent No. 2746474
[0052]
[Patent Document 6]
Japanese Patent No. 2628770
[0053]
[Patent Document 7]
Japanese Patent No. 2628769
[0054]
[Non-patent document 1]
Yoshiharu Inaba, Keno Ueguchi, Tetsuaki Neko, Pressure Waveform Tracking Control in Electric Injection Molding Machine (1st Report)-Application of Learning Control in Flow Pressure Control, "Journal of Precision Engineering", 65, 2, (1999), pp.293-299
[0055]
[Non-patent document 2]
Yoshiharu Inaba, Keno Ueguchi, Tetsuaki Neko, Pressure Control in Electric Injection Molding Machine, "Journal of Precision Engineering", 65, 4, (1999), pp.542-548
[0056]
[Non-Patent Document 3]
Yoshiharu Inaba, Keno Ueguchi, Tetsuaki Neko, Pressure Waveform Tracking Control in Electric Injection Molding Machine (2nd Report)-Application of Learning Control in Pressure Waveform Editing Control, "Journal of Precision Engineering Society", 65, 5, (1999) , pp.746-752
[0057]
[Problems to be solved by the invention]
In FIG. 5, the injection speed command V is applied to the servo amplifiers 40a and 40b of the two servo motors 3a and 3b.^* _iAre supplied with a common speed command pulse train. However, the injection pressure command P^* _i, The pressure detection sensor 10a outputs an analog signal. As a result, the servo amplifiers 40a and 40b output the common analog current command i^* _pWill be given.
[0058]
Therefore, the comparator 43 supplies the motor current command i to both servo motors 3a and 3b.^*As i^* _vIs selected, the amount of movement of the nuts 7a, 7b of both ball screws is guaranteed to be the same by the position control loop of FIG. Therefore, the movable portion 8 does not receive an unreasonable rotational moment from the ball screws 5a and 5b on both sides.
[0059]
However, the motor current command i which the comparator 43 gives to both servomotors 3a, 3b^*As i^* _pIs selected, the same motor current command i is applied to both servomotors 3a and 3b.^* _pIs given, the amount of movement of the nuts 7a and 7b of both ball screws is released from the position control loop of FIG. 5, so that the amount becomes the same due to the difference in load sharing between the ball screws 5a and 5b. That is not guaranteed. For this reason, the movable part 8 may receive an incorrect rotation moment from the ball screws 5a and 5b on both sides. As described above, since the movable portion 8 is generally held by a linear guide that slides on two rails, an improper rotation moment generates excessive lateral stress in the linear guide, and as a result, As a result, the rail may be damaged.
[0060]
In other words, in the two-axis drive control with the structure as shown in FIG. 5, the feedback signal from the motor encoder 11a can be used for the injection speed control, so that the two-axis position synchronization using the position command pulse signal common to the two axes is used. It is possible to control. However, in the torque control for performing the injection pressure control, since the feedback signal is a load cell signal, it is difficult to perform the two-axis position synchronization control, and there is a possibility that the rail may be damaged.
[0061]
In order to prevent such damage to the rails, at present, a master-slave method is employed in which two motor output shafts are mechanically connected by a toothed belt to realize position synchronization control. The master-slave method is a method in which a master servomotor is speed-controlled or torque-controlled, and the other slave motor receives the actual current of the master motor as a current command. However, in such a master-slave system, the size of the machine is easily increased by using a mechanical belt, and it is also necessary to perform maintenance of the mechanical belt.
[0062]
The present invention has been made in view of the above circumstances, and provides a control device for an electric injection molding machine capable of performing position synchronization control by torque control using a multi-axis servomotor without using a mechanical belt. Aim.
[0063]
[Means for Solving the Problems]
In order to achieve the above object, a control device for an electric injection molding machine according to the present invention includes a first screw movement command calculating means for calculating a first screw movement command, and a first screw movement command. A second screw movement command calculation means for calculating a second screw movement command different from the first screw movement command, and comparing the first screw movement command with the second screw movement command, whichever is smaller. An injection control unit including comparison means for selecting one as a final screw movement amount command, and an injection control unit including comparison means for outputting based on the final screw movement amount command selected by the comparison means. It is characterized by having.
[0064]
In order to achieve the above object, a control device for an electric injection molding machine according to the present invention includes a plurality of servomotors, a plurality of ball screws which are rotationally driven by rotation of the plurality of servomotors, and a plurality of Controls an electric injection molding machine including a plurality of nuts that move in the rotation axis direction of the ball screw by the rotation of the ball screw, and a screw that is integrally formed with a movable portion driven by the movement of the plurality of nuts. In the control device of the electric injection device, an injection speed sequence for outputting an injection speed command, and an amount to be moved by the screw during a predetermined control calculation time interval based on the injection speed command output from the injection speed sequence. A converter for calculating as a first screw movement amount command, an injection pressure sequence for outputting an injection pressure command, and an injection pressure detection for detecting an injection pressure. A sensor, an A / D converter receiving an injection pressure detection result from the injection pressure detection sensor, and an injection pressure control deviation from the injection pressure command and the injection pressure detection result input via the A / D converter. And a second screw movement amount that determines the amount by which the screw should move during a predetermined control calculation time interval based on the injection pressure control deviation calculated by the first subtractor. A pressure controller calculated as a command, a comparison between the first screw moving amount command and the second screw moving amount command, and a smaller value output as a final screw moving amount command. And an injection controller including a pulse generator that generates a number of pulses corresponding to the final screw movement amount command output from the comparator as a speed command pulse train at the control calculation time interval, A first counter for counting the number of pulses of the speed command pulse train from the pulse generator and outputting a signal corresponding to the counted number of pulses as a position command, a second counter for detecting the actual position of the motor, A second subtractor for calculating a position control deviation from outputs of the first counter and the second counter; and a position control of the plurality of servomotors based on the position control deviation calculated by the second subtractor. And the same number of servo amplifiers as the plurality of servo motors including a position control loop for performing the control.
[0065]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an internal configuration of a control device for an electric injection molding machine according to one embodiment of the present invention.
That is, the control device according to the present embodiment also includes the injection controller 20 and the plurality of servo amplifiers 40a and 40b. The injection controller 20 corresponds to an “injection control unit” described in the claims. The servo amplifiers 40a and 40b correspond to a "motor control unit" described in the claims.
[0066]
First, the injection controller 20 will be described. The injection controller 20 performs a control calculation every fixed time Δt, and updates the control command.
[0067]
That is, the injection controller 20 of the present embodiment includes an injection speed command time sequence 21, a converter 22, a pulse generator 23, an analog / digital (A / D) converter 25, an injection pressure command time sequence 26, and a subtractor. 27, a pressure controller 28, and a comparator 30. The injection controller 20 is connected to a pressure detection sensor 10a.
[0068]
Here, the converter 22 corresponds to “first screw movement amount command calculating means” described in the claims. Further, the pressure controller 28 corresponds to “second screw movement amount command calculating means” described in the claims, and the comparator 30 corresponds to “comparing means” described in the claims. Further, the injection speed command time sequence 21 corresponds to “injection speed command means” described in the claims, and the injection pressure command time sequence 26 corresponds to “injection pressure command means” described in the claims.
[0069]
In other words, the present embodiment is characterized in that a function corresponding to the comparator 43 is provided not on the servo amplifier side but on the injection controller side. Accordingly, the calculation in the pressure controller 28 is different from that in the example of FIG. 5 described above, and this calculation will be described later in detail.
[0070]
Next, the operation of the injection controller 20 will be described. Injection speed command V from injection speed command time sequence 21^* _iOn the other hand, the converter 22 determines the amount by which the screw 9 should be moved during the time Δt by the screw movement amount command Δx.^* _vIs calculated from the following (Equation 5).
Δx^* _v= V^* _iΔt (Equation 5)
Then, the converter 22 calculates the calculated screw movement amount command Δx.^* _vIs input to the comparator 30.
[0071]
Further, the pressure detected by the pressure detection sensor 10a is used as an injection pressure sensor signal P._iIs taken into the injection controller 20 via the A / D converter 25. The A / D converter 25 receives the injection pressure sensor signal P_iIs input to the subtractor 27.
[0072]
Here, when the pressure detection sensor 10b is attached to the other motor drive shaft, the average value of the output signals of the two pressure detection sensors 10a and 10b is used as the injection pressure sensor signal P_iAnd
[0073]
Further, the injection pressure command time sequence 26 includes an injection pressure command P according to the sequence.^* _iIs input to the subtractor 27. The subtractor 27 sets the injection pressure command P^* _iAnd injection pressure sensor signal P_iControl deviation ΔP_iIs calculated by the following (Equation 6).
ΔP_i= P^* _i-P_i                                  (Equation 6)
Thereafter, the calculated control deviation ΔP_iIs input to the pressure controller 28.
[0074]
The pressure controller 28 determines the control deviation ΔP_iThe PID control calculation is executed to determine the amount by which the screw 9 should advance during the motor Δt time.^* _pIs calculated as Then, the pressure controller 28 calculates the calculated screw movement amount command Δx.^* _pIs input to the comparator 30.
[0075]
The comparator 30 has two screw movement amount commands Δx.^* _vAnd Δx^* _pIs determined by the following (Equation 7).
Δx^*= Min (Δx^* _v, Δx^* _p(Equation 7)
Here, it will be described below that the function corresponding to the above-mentioned comparator 43, that is, the above-mentioned required problem (1) and the above-mentioned required problem (2) can be satisfied by (Equation 7).
[0076]
Injection speed command V^* _iCan be expressed by the following (Equation 8).
(Equation 2)

[0077]
At this time, the screw movement amount command Δx which is the output of the pressure controller 28^* _pIs divided by the time interval Δt to obtain the screw speed command V required for the injection pressure control.^* _pIs obtained by the following (Equation 9).
(Equation 3)

[0078]
By dividing both sides of (Equation 7) by the time interval Δt, the following (Equation 10) is obtained from (Equation 8) and (Equation 9).
(Equation 4)

[0079]
Here, the screw speed command output from the comparator 30 is V^*Then, the following (Equation 11) holds.
(Equation 5)

[0080]
In other words, it can be considered that the function of the comparator 30 is to perform the following operation of (Expression 12) based on (Expression 10) and (Expression 11).
V^*= Min (V^* _i, V^* _p(Equation 12)
At the beginning of the injection, since the resin is not filled in the cavity 12 of the mold 1, the injection pressure is low. For this reason, the injection pressure control deviation ΔP_iBecomes larger. Therefore, the screw movement command Δx which is the output of the pressure controller 28^* _p, In other words, V^* _pBecomes larger. Therefore, in general, V^* _i<V^* _pBecomes At this time, the comparator 30 calculates the final screw speed command V from (Equation 12).^*As V^* _iSelect V^*= V^* _iBecomes This means that the screw movement amount command Δx^* _vMeans that was selected. Therefore, when the injection is started, the injection speed control is prioritized.
[0081]
In addition, during injection speed control, the injection pressure increases and ΔP_iBecomes smaller, the screw movement amount command Δx, which is the output of the pressure controller 28,^* _pIn other words, ΔV^* _pBecomes smaller. That is, V^* _i> V^* _pAt this time, the comparator 30 obtains the final screw speed command V from (Equation 12).^*As V^* _pSelect V^*= V^* _pBecomes This means that the screw movement amount command Δx^* _pMeans that was selected.
[0082]
Therefore, control capable of shifting from injection speed control to injection pressure limitation, that is, control satisfying the above-described required problem (1) can be performed.
[0083]
Also, during the injection pressure control, the injection speed command V^* _iIf becomes smaller, V^* _i<V^* _pBecomes At this time, the comparator 30 obtains the final screw speed command V from (Equation 12).^*As V^* _pSelect V^*= V^* _iBecomes
[0084]
Therefore, control capable of shifting from injection pressure control to injection speed limitation, that is, control satisfying the above-described required problem (2) can be performed.
[0085]
Here, the description returns to FIG.
The comparator 30 calculates the final screw movement amount command Δx by (Equation 7).^*And then this Δx^*Is input to the pulse generator 23. The pulse generator 23 is Δx^*Is generated as a speed command pulse train 24 within the time Δt, and is input to the counter 41 in each servo amplifier.
[0086]
Next, the servo amplifier will be described. That is, the servo amplifier 40a includes counters 41 and 44, subtractors 45 and 48, a position controller 46, a differentiator 47, a speed controller 49, and a pulse width modulation control (PWM) circuit 50. The servo amplifier 40a is connected to the servo motor 3a. Further, a motor encoder 11a is attached to the servo motor 3a.
[0087]
Here, since the injection controller 20 is provided with the comparator 30, there is no need for the servo amplifier shown in FIG.
[0088]
The counter 41 in the servo amplifier 40a which receives the speed command pulse train 24 from the injection controller 20 counts the number of pulses in this pulse train and outputs the position command x of the screw 9.^*Is detected. And this x^*Is input to the subtractor 45.
[0089]
The counter 44 receives a pulse from the motor encoder 11a. The counter 44 counts the number of pulses to detect the actual position x of the screw 9. Then, this x is input to the subtractor 45.
[0090]
The subtractor 45 receives the input x^*And the position control deviation (x^*After calculating −x), the result is input to the position controller 46. The position controller 46 calculates the speed command v according to the following equation.^*Is calculated.
v^*= K_P(X^*−x) (Equation 13)
Where K_PIs a proportional gain of the position controller 46.
[0091]
Note that the motor encoder 11a inputs the pulse to the differentiation circuit 47 in addition to the counter 44. The differentiating circuit 47 detects the actual speed v from this pulse. Then, this v is input to the subtractor 48.
[0092]
The subtractor 48 receives the input v^*Speed control deviation (v^*-V) is calculated and input to the speed controller 49. The speed controller 49 calculates the motor current command i by the following equation.^*Is calculated and input to the PWM circuit 50.
(Equation 6)

Where K_PvIs a proportional gain of the speed controller 49, and T_IvIs the integration time of the speed controller 49.
[0093]
The PWM circuit 50 receives the given motor current command i^*, A predetermined three-phase voltage is applied to the servo motor 3a. As a result, the servo motor 3a receives the motor current i^*Drive with
[0094]
As described above, according to the present embodiment, the same pulse train is output from the pulse generator 23 in the injection controller 20 to the counter 41 in each of the servo amplifiers 40a and 40b of the two servomotors 3a and 3b. Given, and the position control is always performed by the position control loop, so that the two servomotors 3a and 3b have synchronized rotation angles, that is, a two-axis ball screw 5a driven by the two servomotors. , 5b can always be realized during the injection pressure control as well as during the injection speed control.
[0095]
As a result, it is possible to avoid the problem of structural strength due to the synchronization deviation of the two-axis drive that occurs during the injection pressure control without using a mechanical belt.
[0096]
Although the present invention has been described based on one embodiment, the present invention is not limited to the above-described embodiment, and various modifications and applications are possible within the scope of the present invention. Of course. For example, in the above-described embodiment, two servo motors are used, but the present invention is not limited to this. Further, the present invention is not limited to the injection and pressure holding mechanism of the electric injection molding machine, but can be applied to a plasticizing mechanism and a mold opening / closing mechanism.
[0097]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a control device for an injection molding machine capable of performing position synchronization control by torque control using a multi-axis servomotor without using a mechanical belt.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an internal configuration of a control device of an electric injection molding machine according to one embodiment of the present invention.
FIG. 2 is a schematic diagram of an injection / pressure keeping mechanism driven by two axes in an electric injection molding machine.
FIG. 3 is a schematic diagram of a control device of the electric injection molding machine.
FIG. 4 is a timing chart for explaining the operation of the control device of the electric injection molding machine.
FIG. 5 is a block diagram showing an internal configuration of a control device of a conventional electric injection molding machine.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 mold, 2 injection cylinder, 3a, 3b servo motor, 4a, 4b reduction gear, 5a, 5b ball screw, 6a, 6b bearing, 7a, 7b nut, 8 movable part, 9 screw , 10a, 10b ... pressure detection sensor, 11a, 11b ... motor encoder, 12 ... cavity, 20 ... injection controller, 21 ... injection speed command time sequence, 22 ... converter, 23 ... pulse generator, 25, 42 ... analog / Digital (A / D) converter, 26 ... Injection pressure command time sequence, 27, 45, 48 ... Subtractor, 28 ... Pressure controller, 29 ... Digital / analog (D / A) converter, 30, 43 ... Comparator, 40a, 40b Servo amplifier, 41, 44 Counter, 46 Position controller, 47 Differentiator circuit, 49 Speed controller, 50 Pulse width modulation control (PWM) circuit

Claims (4)

A first screw movement command calculating means for calculating a first screw movement command, and a second screw movement command calculation for calculating a second screw movement command different from the first screw movement command An injection control unit comprising: means for comparing the first screw movement amount command and the second screw movement amount command, and selecting a smaller one as a final screw movement amount instruction; ,
A plurality of motor control units that perform position synchronization control of a plurality of motors based on a final screw movement amount command selected by the comparing unit,
A control device for an electric injection molding machine, comprising: Injection speed command means for outputting an injection speed command for commanding an injection speed,
Injection pressure command means for commanding the injection pressure;
Has,
The first screw moving amount command calculating means calculates the first screw moving amount command based on the injection speed command output by the injection speed commanding means, and the second screw moving amount command calculating means calculates The control of the electric injection molding machine according to claim 1, wherein the second screw movement amount command is calculated based on a difference between the injection pressure command output by the injection pressure command means and the actual injection pressure. apparatus. 2. The motor according to claim 1, wherein the motor control means includes a position control loop for performing position synchronization control of a plurality of motors based on a final screw movement amount command output from the comparison means. Control device for electric injection molding machine. A plurality of servomotors, a plurality of ball screws rotationally driven by the rotation of the plurality of servomotors, a plurality of nuts moving in the rotation axis direction of the ball screws by the rotation of the plurality of ball screws, and the plurality of nuts In a control device of an electric injection device that controls an electric injection molding machine configured by a movable unit driven by the movement of the screw and a screw that is integrally formed,
An injection speed sequence for outputting an injection speed command, and an amount by which the screw should move during a predetermined control calculation time interval based on the injection speed command output from the injection speed sequence is defined as a first screw movement amount command. A converter for calculating, an injection pressure sequence for outputting an injection pressure command, an injection pressure detection sensor for detecting an injection pressure, an A / D converter receiving an injection pressure detection result from the injection pressure detection sensor, A first subtractor for calculating an injection pressure control deviation from a pressure command and an injection pressure detection result input via the A / D converter, and an injection pressure control deviation calculated by the first subtractor. A pressure controller that calculates an amount by which the screw should move during a predetermined control calculation time interval as a second screw movement amount command, based on the first screw movement amount command; A comparator for comparing the second screw movement command with the second screw movement command and outputting the smaller value as a final screw movement command; and a final screw movement command output from the comparator. An injection controller including a pulse generator that generates a number of pulses corresponding to the above as a speed command pulse train at the control calculation time interval,
A first counter that counts the number of pulses of the speed command pulse train from the pulse generator and outputs a signal corresponding to the counted number of pulses as a position command, a second counter that detects the actual position of the motor, A second subtractor for calculating a position control deviation from outputs of the first counter and the second counter; and a position control of the plurality of servomotors based on the position control deviation calculated by the second subtractor. The same number of servo amplifiers as the plurality of servo motors including a position control loop that performs
A control device for an electric injection molding machine, comprising:

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