【正文】 Effects of feedforward control In the case of position feedback only, increasing gain K to decrease error DZ causes oscillation due p to the time delay in the system, as shown by AOFFB in Fig. 13. That is, K cannot be increased. Applying the feedforward of the arm lever value described in Section can decrease error without increasing K as shown by AONB in the figure. p . Effects of pensation in attitude Level crowding is apt to bee oscillatory at the raised position or when crowding is almost pleted. This oscillation can be prevented by changing gain K according to the attitude, as has been p discussed in Section . The effect is shown in . This shows the result when the level crowding was done at around 2 m above ground. Compared tothe case without the pensation, denoted by OFF in the figure, the ON case with the pensation provides stable response. Fig. 14. Effect of adaptive gain control on control error of Z. . Effects of control inter213。采用這種機(jī)器進(jìn)行挖掘和裝載操作，要求司機(jī)要具備高水平的操作技能，即便是熟練的司機(jī)也會產(chǎn)生相當(dāng)大的疲勞。 如果司機(jī)只要操控一 個操作桿，而其它自由桿臂自動的隨動動作，操作就變得非常簡單。 2．液壓挖掘機(jī)的模型 為了研究液壓挖掘機(jī)的控制算法 ,必須分析液壓挖掘機(jī)的數(shù)學(xué)模型。 。 滑閥的反應(yīng)特性 滑閥動作對液壓挖掘機(jī)的控制特性產(chǎn)生會很大的影響。這一類閥中，閥芯的位移與閥的開度是非線性的關(guān)系。為了避免這個問題，改用液壓缸力反饋取代加速度反饋（圖 4 的下環(huán)）。通過調(diào)整改變前饋增益 Kff，可實現(xiàn)最佳的前饋率。）圖 8 表示其中一組結(jié)果。 為獲得高速度、高精度控制，在控制器上采用數(shù)字處理芯片，傳感器上使用高分辨率的磁編碼器。 （ 2）鏟斗水平舉升模式：用鏟斗水平舉升切換開關(guān)，在手控動臂舉升操作中，系統(tǒng)自動控制鏟斗。的梯度從最初始值開始改變其參考角度值，測量其反應(yīng)，從而確定第 3 節(jié)所描述的控制算法的作用。 反鏟水平控制測試 在不同的控制和操作位置下進(jìn)行控制測驗，觀察其控制特性，同時確定最優(yōu)控制參數(shù)（如圖 6 所示的控 制放大系數(shù)）。 控制間隔的作用 關(guān)于控制操作的控制間隔的作用，研究結(jié)果如下： 100ms 時，不穩(wěn)定振蕩因運(yùn)動的慣性隨位置而加劇。 將這些控制技術(shù)應(yīng)用在其它結(jié)構(gòu)的機(jī)器上，如履帶式起重機(jī)，能使普通結(jié)構(gòu)的機(jī)器改進(jìn)成為可讓任何人容易操控的機(jī)器。同時也證實了非線性補(bǔ) 償能使普通控制閥應(yīng)用在自動控制系統(tǒng)中。圖 14 表示其作用，表明反鏟在離地大約 2 米時水平動作結(jié)果。加入加速度或壓力反饋后，響應(yīng)的穩(wěn)定性得到改進(jìn)。 單個組件的自動控制測試 對于動臂、斗柄、鏟斗每一組件，以 177。在這種情況下，當(dāng)斗柄操作桿開始操控時，其參考位置是從地面到斗柄底部的高度。 控制器是采用 16 位 的微處理器，能接收來自動臂、斗柄、鏟斗傳感器的角度輸入信號，控制每一操作手柄的位置，選擇相應(yīng)的控制模式和計算其實際改變量，將來自放大器的信號以電信號形式輸出結(jié)果。 5 模擬實驗結(jié)論 反鏟 水平動作控制的模擬實驗是將本文第 4 節(jié)所描述的控制算法用在本文第 2 節(jié)所討論的液壓挖掘機(jī)的模型上。 前饋控制 由圖 1 計算 Z，可以得到 將方程（ 8）兩邊對時間求導(dǎo)，得到以下關(guān)系式， 右邊第一個式子看作是表達(dá)式（反饋部分）將 替換成 1，右邊第二個式子是表達(dá)式（前饋部分）計算當(dāng) θ2手動地改變時， θ1的改變量?？梢?，利用加速度反饋來提高反應(yīng)特性效果明顯。 非線性補(bǔ)償 在普通的自動控制系統(tǒng)中，常使用如伺服閥這一類新的控制裝置。 連桿關(guān)系 在圖 1 所示模型中，液壓缸長度改變率與桿臂的旋轉(zhuǎn)角速度的關(guān)系如下： (1)動臂 (2)斗柄 (3)鏟斗 當(dāng) 時， 扭矩關(guān)系 從 節(jié)的連桿關(guān)系可知，考慮到液壓缸的摩擦力，提供的扭矩 τi如下 其中， Cci是粘滯摩擦系數(shù) 。可作如下假設(shè)： 。而且我們已采用這種控制算法，設(shè)計出了液壓挖掘機(jī)的半自動控制系統(tǒng)。 例如，液壓挖掘機(jī)的反鏟水平動作，必須同時操控三個操作手柄（動臂，斗柄，鏟斗）使鏟斗的頂部沿著水平面（圖 1）運(yùn)動。依照此法，可通過正反饋及前饋控制、非線性補(bǔ)償、狀態(tài)反饋和增益調(diào)度等各種手段獲得較高的控制精度和穩(wěn)定性能。idual attachments For each attachment of the boom, arm, and bucket, the reference angle was changed 58 stepwise from the initial value, and the responses were measured。 γ soil density。 mean boom arm, and bucket, respectively.) . Hydraulic model Each joint is driven by a hydraulic cylinder whose flow is controlled by a spool valve, as shown in Fig. 3. We can assume the following: 1. The open area of a valve is proportional to the spool displacement. 2. There is no oil leak. 3. No pressure drop occurs when oil flows through piping. 4. The effective sectional area of the cylinder is the same on both the head and the rod this problem, for each joint, we have thefollowing equation from the pressure flow characteristics of the cylinder: when, where, Ai seffective crosssectional area of cylinder。 Hydraulic shovel。Psi ssupply pressure。 This system has a paratively small coefficient , so the response is oscillatory. For instance, if in our large SK16 hydraulic shovel, X10 is 0, the coefficients are given as a =10y2 , ,a1= 10 ,a2= 10 . Addingthe acceleration feedback of gain Ka , to this the upper loop in Fig. a 4., the closed loop transfer function is given as Adding this factor, the coefficient of s2 bees larger, thus, the system bees stable. In this way,acceleration feedback is effective in improving the response characteristics. However, it is generally difficult to detect acceleration accurately. To overe this difficulty, cylinder force feedback was applied instead of acceleration feedback the lower loop in Fig. 4.. In this case, cylinder force is calculated from detected cylinder pressure and filtered in its lowerfrequency portion[]. This is called pressure . Servo control system When one joint is manually operated and another joint is controlled automatically to follow the manual operation, a servo control system must be required. For example, as shown in Fig. 6, in the level crowding control, the boom is controlled to keep the arm and height Z (calculated from 81 and 82 ) tor. In order to obtain more accurate control, the following control actions are introduced. . Fe