AbstractA concept of digital control system to assist the operators of hydraulic excavators is presented and discussed. Then, control system based on described ideas was mounted on a special numerically controlled stand, equipped with D r A and A r D converters, where small hydraulic backhoe excavator K-111 fixtures were used. Experimental results shows that it fulfils all described requirements and can be used as the machine operator assist. It enables for precision tool guidance. automatic repetition of realized movements, realization of specific tool trajectories including energetically optimal path sand automatic improvement or optimization of realized paths. Tool trajectories can also be prescribed using the setting model, making excavator the machine of tele operator class. Presented system can be used as a basis for real machine control system. q 1998 Elsevier Science B.V. All rights reserved.Keywords: Digital control system; Hydraulic excavators; Tool trajectories1. IntroductionThe automation of heavy machines, including hydraulic excavators, began in mid-1970s and waspossible due to invention of real time controllers and hydraulic elements with good dynamic properties. The first excavator equipped with several mechatronics systems, which was shown as a working model, was the excavator FUTURE prepared by Orenstein and Koppel for BAUMA83 Fairs. Since that time, machines equipped with systems automating the engine operation, pumps operation, machine fixtures, machine diagnostic, etc., are presented and offered. Such systems bring real help to the operator and clear economical profit. For example, LIEBHERRR902 excavator equipped with LITRONIC System. has for a trench digging the efficiency 40% higher and unit costs 30% lower, than similar machine without such automatic system. Although automation . in some case, optimization of several machine systems develops quite fast, the main machine processthe shoving processhas no proper understanding and description until now. Its automation is quite limited to systems repeating already performed. movements, laser levelling systems, etc. and systems optimizing such processes are not developed yet. Quite new experimental results show clear idea for energetically optimal tool trajectories in the case of cohesive materials. The tool tip has to be guided along slip lines, which are generated from the tiptool during the previous stage of the shoving process. To realize such trajectories for practical purpose and real machines, it is necessary to build a special control system for the tool motion, which enables automatic realization of such trajectories as well as realization of other tasks that help the operator.2. The basic concept of the computer aided control systemItIt was shown before that analyzing the the soil deformation during the shoving process, it is possible to determine energetically optimal cutting tool trajectories. Hence, the automatic tool movement along slip lines generated in cohesive material has to be a quite important option of proposed system. It should also enable precision tool guidance, automatic repetition of already realized movements . for example, teach-in , realization of some tool movements impossible to realize manually, etc. Taking into account to-day experience with automation of heavy machines, such system should be constructed to assist machine operator, who still plays a main decisive and control role. Hence, the proper separation of tasks, between the control sys-tem and the operator, is necessary. Such control system for excavators was built on laboratory scale. Its basic assumptions can be stat d w x . as follows 13 : 1 operation of the central control system is based on cooperation of two digital systems. The first one controls directly the motion of the machine fixture using the control system of the hydraulic cylinders position. The second one works . out control signals for the first one. 2 Under the standard work conditions, action of the proportionalhydraulic valves of the fixture cylinders is controlled through the computer. The direct operator control is . possible only in case of emergency conditions. 3The feedback between the machine environment and control system is realized through the operator. He participates continuously in the process of the con- . control of machine fixtures motion. 4 For realization of the tool motions which are impossible for manual control, the operator has a possibility to coordinate displacement of separate cylinders by means of hard- . ware or software. 5 The operator has a possibility to switch into automatic control of the fixture motionto realize a special tool trajectories. For example, it can be energetically optimal tool trajectory where tool tip moves along slip lines or specific trajectory . realized and stored previously. 6 The optimal cut-ting tool trajectories can also be realized as correction of trajectories given by the operat