Control Testing

Non Pressure-Compensated Control

As of 5/25/04, the backhoe can successfully track both the PHANToM and a computer generated trajectory without unwanted vibrations. These vibrations were eliminated by rebuilding the PVG32 valves without pressure compensation. See data file for tracking and pressure data.

Four Degree of Freedom Haptic Control

Haptic position control video (avi 22M)

Haptic position control animation (avi 13M)

Simulink control model

Position tracking data

workspace transformations:
backhoe - PHANToM position mapping

The PHANToM was programmed to generate a reference position command for the backhoe and simultaneously display haptic forces on the hand of the operator proportional to position error. The video clip on the left shows the backhoe and PHANToM operating under haptic position control using bilateral communication. The second video clip from the left illustrates the same motion animated in Pro/ENGINEER. The third figure from the left is a snapshot of the top-level diagram of the Simulink model that runs the backhoe in real time. The fourth figure from the left shows the position tracking data from the video on the left in cylinder coordinates. The figure on the right illustrates the workspace transformations that map backhoe into the PHANToM's workspace and vice versa. See also the thesis presentation.

Four Degree of Freedom Computer Control

sinusoidal swing reference (avi 8.8M)	sinusoidal boom reference (avi 9.6M)		sinusoidal stick reference (avi 9.9M)	sinusoidal bucket reference (avi 9.9M)		"trenching" trajectory reference in free space (avi 31M)
input / output data illustrating swing & boom oscillations		open-loop data used to program feed-forward controller			boom oscillations removed w/feedforward control
Simultaneous feedback control of all four degrees of freedom was first achieved on 3/28/04 using computer generated commands and controlling cylinder lengths. The first four video clips above show the response of each function to a sinusoidal reference, and the last clip shows the response to a trenching trajectory reference in free space. Initial results show that oscillations occur while under feedback control when the valve spools are displaced in the negative direction (only). These oscillations do not occur while under manual control. See the report with data on backhoe vibrations. Further testing showed that the boom oscillations could be removed by using a feed-forward control block, but this was only successful when using computer generated reference commands because of the necessity to take numerical derivatives of the reference to generate a voltage command based on the desired cylinder velocity. When feed-forward control was attempted with the PHANToM, the system became unstable from noise in the encoders, even after aggressive filtering.

Single Degree of Freedom Haptic Control

As of 10/29/03, closed-loop haptic control has been achieved on the backhoe using the PVG32 EH proportional valve, PHANToM haptic manipulator, and a controller written in Matlab/Simulink/xPC-Target. A virtual spring connects the dipperstick cylinder position to the y-axis (vertical) motion of the PHANToM.

Haptic Backhoe Control System

Single DOF Video

The video clips to the right illustrate the backhoe under closed-loop haptic control. The virtual spring connection could be clearly felt as the backhoe followed the motion of the PHANToM.

Video Clip 1 (avi 4.7M)

Video Clip 2 (avi 7.0M)

Marginal Undamped Stability

In the video clip to the right, marginally stable behavior was observed when the joystick was unconstrained and given an impulse. Note that for these tests, there was no virtual damping coupled with the virtual spring connection.

Video Clip 3 (avi 4.5M)

Closed-Loop Data

The plot to the right shows the response of the dipperstick cylinder when given a computer generated sinusoidal input.

A simple closed-loop proportional feedback control program was written, with cylinder length as the reference input and the measured cylinder length as the output. Here the reference input was a 2in sine wave at 0.4Hz. Cylinder length measurements were taken with a Temposonics magnetostrictive position sensor.

Dipperstick closed-loop response @ 0.4Hz