【正文】 g ithe fulcrum and the center of gravity, mi is the mass of the attachment, Ii is the moment of inertia around (the center of gravity subscripts is1–3。 hi scylinder length。Psi ssupply pressure。 Pi scylinder rodside pressure。 Bi sspool width。 Ksbulk modulus of oil。 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. . Feedforward control Calculating Z from Fig. 1, we obtain Differentiating both sides of Eq.(8). with respect to time, we have the following relation, The first term of the righthand side can be taken as the expression (feedback portion) to convert Z˙ to , and the second term of the righthand side is the expression (feedforward portion)to calculate howmuch u should be changed when u is changed , u˙ is determined using the difference value of Du . To optimize the feedforward rate, feedforward gain K is tunned. ff There may be a method to detect and use the arm operatinglever condition iangle. instead of arm angular velocity, since the arm is driven at an angularvelocity nearly proportional to this lever condition. . Adapti213。 determines the condition of each control lever。 and outputs the results from the amplifier as electrical signals. The hydraulic control system generates hydraulic pressureproportional Fig. 8. Simulation result of level crowding. to the electrical signals from the electromagic proportionalreducing valve, positions the spool of the main control valve, and controls the flow rate to the hydraulic cylinder. In order to realize highspeed, highaccuracy control, a numeric data processor is employed for the Fig. 9. Effect of feedforward control on control error of Z. Fig. 10. Schema of control system. controller, and a highresolution magic encoder is used for the sensor. In addition to these, a pressure transducer is installed in each cylinder to achieve pressure feedback. The measured data are stored up to the memory, and can be taken out from the munication port. . Control functions This control system has three control modes,which are automatically switched in accordance with lever operation and selector switches. These functions are the following (1). Level crowding mode: during the manual arm pushing operation with the level crowding switch, the system automatically controls the boom and holds the arm end movement level. In this case, the reference position is the height of the arm end from the ground when the arm lever began to be operated. Operation of the boom lever can interrupt automatic control temporarily, because priority is given to manual operation. (2) Horizontal bucket lifting mode: during the manual boom raising operation with the horizontal bucket lifting switch, the system automatically controls the bucket. Keeping the bucket angle equal to that at the beginning of operation prevents material spillage from the bucket. (3) Manual operation mode: when neither the level crowding switch nor the horizontal bucket lifting switch are selected, the boom, arm, and bucket are controlled by manual operation only. The program realizing these functions is primarily written in C language, and has wellstructured module to improve maintainability. 7. Results and analysis of field test We put the field test with the system. We confirmed that the system worked correctly and the effects of the control algorithm described in Chaps. 3 and 4 were a