This paper describes a collision avoidance system using Whole Arm Proximity (WHAP) sensors on a PUMA 560 robot arm. The capacitance-based sensors generate electric fields which can completely encompass the robot arm and detect obstacles as they approach from any direction. The directional obstacle information gathered by the WHAP sensors together with the sensor geometry and robot configuration is used to scale the commanded joint velocities of the robot. A linearized relationship between the WHAP sensor reading and the distance from the obstacle allows direct transformation of perturbations in VHAP readings to perturbations in joint velocities. The VHAP reading is used to directly reduce the component of the command input velocity along the normal axis of the sensor, allowing graceful reductions in speed as the arm approaches the obstacle. By scaling only the component of the velocity vector in the,direction of the nearest obstacles, the control system restricts motion in the direction of obstacles while permitting unconstrained motion in other directions.

A sensor-based control approach for real-time seam tracking of rocket thrust chamber assemblies has been developed to enable automation of a braze paste dispensing process. This approach utilizes a non-contact multi-axis seam tracking (MAST) sensor to track the seams. The MAST sensor measures capacitance variations between the sensor and the workpiece and produces four varying voltages which are read directly into the robot controller. A PID control algorithm which runs at the application program level has been designed based upon a simple dynamic model of the combined robot and sensor plant. The control algorithm acts on the incoming sensor signals in real-time to guide the robot motion along the seam path. Experiments demonstrate that seams can be tracked at 100 mm/sec within the accuracy required for braze paste dispensing.>

The authors address the issue of collision avoidance in unknown or partially modeled environments using a capacitative sensor. An eight channel capacitance-based sensor system which can detect obstacles up to 400 mm away has been developed. This sensor can detect both conductive and nonconductive obstacles of arbitrary color and shape. The sensor hardware was reliable and inexpensive, and may be fabricated using flexible printed circuit boards to provide whole-arm and joint protection for any robot or manipulator. Simple collision avoidance control algorithms have been implemented on a two-link robot arm. The sensor and control system enable the robot arm to avoid a conductive post and a concrete block.>

A high-resolution capacitive image sensing technique for measuring edge and surface profiles during manufacturing processes has been invented. A prototype device utilizing this technique consists of two 500- mu m-diameter electrodes fabricated on a printed circuit board with a 250- mu m gap between them. As the device is mechanically scanned over the workpiece, the spatial variations in the edge or surface to be measured interfere with an electric field imposed between the electrodes, altering the mutual capacitance. The sensor functions as a near-field proximity sensor, producing range images of surface imperfections. This sensor has been used in applications requiring a preview image of burns on the edge of a machined part and other processes requiring an inspection image after automated deburring operations.>

Initial experiments characterizing a shunt-mode sensor that simultaneously measures both normal and shear strains due to an applied force vector have been completed. The sensor, termed SCCINS (sensed capacitance changes due to incident normal and shear stress), is based on variations in the physical dimensions of an elastic dielectric due to applied forces. Two sinusoids of the same frequency but with a fixed phase relationship are used to excite the device. The amplitude and phase of the output signal are modulated by normal and shear strains, respectively. By measuring the amplitude and phase of the output signal, these strains may be determined, and subsequently used to reconstruct the normal and shear components of the force vector.>