Simplified Vector-Directed Control of a Tiltrotator Equipped Excavator

Abstract

A tiltrotator is an attachment for an excavator, inserted between the excavator arm and the bucket. It attaches to and utilizes the excavator's native bucket motion actuator to provide angular motion in the motion plane of the excavator arm. The tiltrotator then adds a joint with the ability to tilt ±45° perpendicular to the excavator arm, and an additional joint permitting 360° rotation normal to the previous joint axis. [1] The tiltrotator expands an excavator's range of motion, but also increases the number and complexity of the operator's controls. This thesis applies principles of robotics to a tiltrotator-equipped excavator, allowing the operator to directly control the velocity vectors describing the excavator bucket position and orientation instead of controlling them indirectly through the manipulation of individual joints. The proposed user input method for the excavator utilizes a pair of 3D mice, with one mouse directing velocity along the x,y,z (or r,θ,z) axes and bucket digging motion, and the other mouse directing the bucket orientation. Using directional vectors obtained from these mice, individual joint angles and velocities are manipulated automatically to move the bucket in the direction and orientation specified by the user. Two closed loop excavator joint control methods are examined: velocity control and time-sliced positional control. The former is more accurate and mathematically elegant, and the latter is simpler and less computationally-intensive. The results of these two methods will be compared to assess their strengths and weaknesses experimentally.