Wheelchair-Mounted Manipulator

The use of robotic manipulators to augment upper extremity function has been limited by the availability of a means to control multiple degrees of freedom simultaneously to generate smooth and efficient movements. This development project employs multi-degree of freedom human-computer interfaces in an effort to convey a child’s input to the motion of a manipulator.

Design and Development
Implementation of four different controllers:
Stylus
- Six degrees of freedom
- Revolute joints, same configuration as iARM manipulator
- Input: one-to-one angles matching. Does not require inverse kinematics
- Toggle button for grasping
- Forward kinematics used in the collision detection algorithm for interaction with objects

Spaceball
- Six degrees of freedom
- Input: Isometric forces and torques that are interpreted as end-effector linear and angular velocities.
- Inverse kinematics: Inverse Jacobian to determine joint angles.
- Manipulability of the end-effector to handle singularities
- Forward kinematics used in the collision detection algorithm for interaction with objects
- Toggle buttons for grasping and stopping the simulation

Joystick
- Three degrees of freedom plus toggle button to switch between translation and rotation (i.e., position and orientation)
- Input: Normalized angle value that is interpreted as the value of displacement or rotation.
- Inverse kinematics for a 6 dof revolute joint manipulator
- Forward kinematics used in the collision detection algorithm for interaction with objects
- Toggle button for grasping and stopping simulation
- Algorithm for singularities still pending.

Flock of Birds
- Magnetic-field tracking position device
- Six degrees of freedom
- Input: Position and angles of a magnetic sensor related to a reference frame determined by the position of a transmitter.
- Inverse kinematics for a 6 dof revolute joint manipulator.
- No collision detection algorithm implemented

Current Work
- Extend reaching and grasping abilities to accomplish a large number of tasks in an unstructured world by making use of a variety of control algorithms including direct multi-joint position control, resolved Cartesian rate control via force input, and hybrid Cartesian/joint methods for isometric force input ball (Spacemouse 5000®) and position sensing six degree of freedom stylus (Immersion Probe®) controllers. January 2007.
- Implement two alternative controllers for evaluation, Flock of Birds (Ascension Tech) and three degree of freedom joystick. January 2008
- Create training environment and evaluate controllers using box of blocks function test and Fitts' law paradigm test. January 2008.

Experimental design
- Shutter glasses are used to create the 3D image, Virtual Reality Modeling Language (VRML), position sensing six degree of freedom stylus, isometric force input ball, and Matlab are the main technological components of the three dimensional virtual training system.
- Box of blocks function test and Fitts' law paradigm test
- The experiments were conducted on 6 subjects, 4 female, two male. Two-day experiment.
- The first day consisted of all of the real life experiments, and two fifteen minute training session in virtual reality, one session per user interface (Stylus and Spaceball). The second session consisted of exact duplicates of the real life tests in virtual reality.
- Data collected from position tracking devices and the programs controlling the visual representations

Results
- Fitts’ law shows that the movement time is dependant on ID.
- The most significant source of variation is the input device
- Stylus presented a more realistic approach to the normal human movements whereas Spaceball was characterized by continuous overshooting in reaching the targets, mainly due to the non familiarity of the subject with the behavior of the device.
- Box of blocks displayed a better behavior of the subject when using the Spaceball than Fitts’ Law test, in terms of time and accuracy; this could be attributed to the fact that in a more realistic environment the awkwardness of the movements are less relevant.