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The excavation process has got two main features. The first one is the soil digging. It can be regarded as a quasi-static process in fact, in which the acceleration could be neglected. The second one is the soil transportation and bucket discharging. It can be considered as a dynamic process. Some parts of these features would be automated. There are two main control systems, open and closed-loop control. The main aim of the paper is to present the application of these two systems and compare them. The control systems were tested during the digging process. It begins with the bucket on the primary digging position and ends when it is filled. The paper starts with description of the excavator control systems components. They have got hierarchical structure. The first is the hardware level: sensors, actuators, valves. The PLC executes a direct control on this level. The links between objects would be realized via CAN network. The excavator's control system realizes a simple excavator's bucket motion along prescribed trajectory algorithm. The software level assures calculation of the trajectory parameters, i.e. coordination of the milestones. The bucket velocity was the input quantity. It means that the valve's spool displacements are calculated for each actuator separately. Machine counterbalance and actuators parameters would be the limits of the process. The results of the two systems testing procedure would be presented and compared.

ABSTRACT.Recently, there is an increasing interest in controlled excavation processes. However, the main attention, in research works, is paid to the bucket motion. This part of the process can be considered as a quasi static, kinematically induces process 8. It means that dynamic effects, by dropping accelerations terms can be neglected. This is not a case in the second part of the process consisting of: lifting the bucket filled with the soil, swinging the whole excavator with respect to vertical axis, lowering the bucket and discharging it. Next, the bucket is brought back to the excavation place again. Discussing these motions, one has to taking in to account dynamic effects. It should be also noted that mentioned motions are lasting approximately the same time as the digging process. It is then worthy to try to minimize the time needed for bringing the filled bucket to the discharge place, and back to the digging site. It is then the aim of the paper to present an optimal control of such a minimum time process. The paper deals with an optimum problem of positioning an excavator bucket along prescribed trajectory using minimum time. The paper is illustrated with numerical results giving some optimal trajectories.

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The study presents a practical, optimal control system of the discharge process of a backhoe bucket. The process begins when the bucket is filled and ends when the bucket come back to the digging position. In the process, several geometrical constraints are considered, such as, clearance dimension, and obstacles in the excavator working zone. In other words, the operator has to give the path of the discharge process. The problem is considered as a multi body, chain system, driven by hydraulic actuators. The system is decomp osed in free body diagrams of separate elements. Starting from the bucket, each element is solved separately, as many times, as many it is needed to get optimal time for given actuator forces.