Studies on task planning for scooping of piled ore by wheel loader

SUMMARY

The purpose of this research is development of basic method for task planning of operation of Wheel Loader (Front End Loader: it will hereinafter be abbreviated "loader") in combination with dump trucks. Loading operation by the combination of loader and dump trucks is one of the major loading method in surface mines. The unmanned operation of dump trucks has been applied in daily mining operation in several mines. Contrast with that, the unmanned operation of loader has just entered the stage of basic research. The operation of loader involves the contact and interaction with the environment such as rock, rough terrain etc. Especially, task planning including decision of scooping position has been stayed in conceptual studies.

For the unmanned operation, working environment of mining field is Irregular shaped Heavier Material Environment (IHME). IHME is formed with irregular shaped material such as fragmented rock, sand or soil. The pile changes its shape with advancing the mining operation. The unmanned system in IHME should be an intelligent system which can decide the action based on the changing situation.

Structure of the developing system is the model based system as a prerequisite. The model based system is one of the structure of an intelligent system. It is a method for decision making and motion control through processing the models which are integral expression of the environment and motion of the system. The most significant character of the model based system is that the system can understand the present state in the executing task. The action of the model based system separated into two phases: the task planning phase and the execution phase. The aim of this research is development of task planning method for the model based system.

Task planning is a transformation from task level specification into motion level specification. The task plan is series of reference value from the given initial state to the desired final state. Loading operation consists of several cycles of scooping and traveling motion. The output of the task planning is series of scooping and traveling motion. Each scooping and traveling motion is described as reference value for the motion controller.

In the first step of the research, models for environment and motion are developed. Then the task planning method employing these model has been developed.

The column model has been developed for description of shape and behavior of the piled ore. The working place is tessellated into sections which are bases of columns. The height of the column represents the height of ore. However, the size of section and unit height of column is not coincident with particle of ore. In the column model, change of shape and falling behavior due to scooping are expressed as transfer of height unit between columns.

Bucket motion model and V shape model as travel model of the loader have been developed. These models express major motion of the loader. The bucket motion trajectory is generated using the bucket motion model and is expressed as the reference value for each joint of bucket link mechanism. The bucket motion model which consists of three sections is formed based on motion measurement of real loader. By setting parameters such as bucket capacity, slope inclination of the pile etc., the bucket path is generated based on the shape of piled ore at scooping point.

V shape path model is used for generation of travel path between scooping point and dumping point. By the model, travel path is generated for given position and direction at both end points of the path.

If scooping position and direction are given, bucket trajectory and travel path are generated through processing these models. It is necessary to determine the position and direction of each scooping point for the planning of scooping motion series from the initial state to the final state. Criteria for scooping position selection are follows; 1. points in neighbor of previous scooping point. 2. point makes length of edge minimum after scooping.

This report consists of seven chapters. Chapter 1 is an introduction of this report. The background of this studies is outlined and the subjects are introduced. From chapter 2 through 5, the models for the task planning are described. The models include the piled ore model, the bucket motion model and the travel path model.

In chapter 2, the column model is developed for description of the shape and falling behavior of piled ore. In chapter 3, the method for generation of the column model based on measurement is described.

In chapter 4, the bucket motion model for generation of reference bucket path is described. In chapter 5, V-shape model which is travel path model between scooping point and dumping point is discussed. I

In chapter 6, generation method of task planning is described. By the processing the models, scooping position and direction for each scooping are decided and the series of scooping motion for scoop up the whole piled ore is generated.

Chapter 7 is conclusion of the report.