Computer Engineering Department

Robotics Laboratory

Professor Mayez Al-Mouhamed

Research Theme

Anthropomorphic Force-Reflective Master-Slave System

Motivation

• A light, anthropomorphic, back-drivable, transmission mechanism for telerobotics
• Fidelity and sensitivity to small force/torque feedback magnitudes
• Effective mechanisms, transparency, compactness, and low cost.

Approach

Figure 1: Anthropomorphic, 6 dof arm, without the driving cables

1. Multiple Loop Transmission

    

   1. Multiple Cable Pulley Loop mechanism (simplicity, maintainability)
   2. Each CPL is an independent system and can be locally maintained.
   3. A loop starts with a threaded roller at motor shaft
   4. Embedding the wire in the thread eliminates slippage
   5. Both ends of the rope are wrapped around the driven wheel
   6. Wire is wrapped 2 times to provide an acceptable range of motion
   7. In the final wrap, the rope is restrained from any slippage
   8. Pre-tensioning the wire is done independently for each loop
   9. High-speed, low tension cable until the last transmission stage where a high tension is used at the link level

2. Backdrivable Mechanism

    

   1. Low gear, light mechanism, minimal friction
   2. Decoupled rotative joints with no backlash due to the pre-tensioning
   3. Reducers are placed as close as possible to driven links.

                                  Fig. 2: Decoupled structure

3. Motor Grounding

1. All motors are grounded to improve arm dynamics.
2. Low friction cable routing structure within the first link for uncoupling (dof 1 and 4)
3. The motor-link transmission is based on cable-pulley arrangement.

                     Figure 2: Threaded driving rollers and guiding system

4. Kinesthetic Force Feedback

1. Anthropomorphic: direct position-force mapping to human arm 
2. Improved motion mapping: hand center at 3 concurrent rotation axes 
3. Low friction, low inertia, uncoupled dofs (3 Kgs arm weight)
4. Kinematic model: rendering Cartesian position, display force, mapping hand to remote tool.

                      Figure 3: Hand center at the concurrency center of last three dofs