The tactile sensor demonstrator, the sensors on the RobotiQ hand and sensors for the SRI/Meka/Stanford ARM-H hand share a common design. The normal+shear sensor used for adhesion sensing also shares common design elements.
![](http://bdml.stanford.edu/uploads/Main/CapacitiveSensorDesign/sensorstructure.jpg)
The structure of the tactile sensors is shown at right. A multi-layer rigid or flexible PC board provides grounding and shielding. The upper surface is also grounded, to reduce noise and prevent the sensor from functioning as a proximity sensor. The sensor uses Analog Devices AD7147-1 chips to read the taxels, provide filtering and active shielding and communicate via I^2C bus. Small arrays of n sensors can be sampled at 1200/n Hz. Not shown is an upper layer of protective skin. The skin thickness will vary according to application, and the gripping surface will typically be textured for repeatable sliding performance.
![](http://bdml.stanford.edu/uploads/Main/CapacitiveSensorDesign/mfgprocess.jpg)
The manufacturing process for the dielectric is shown at right. A conductive mesh fabric is placed atop a mold and silicone rubber is pushed through it into the mold, forming an array of posts. For the demonstrator boards and RobotiQ hand, the post material is a silicone RTV with a durometer of Shore A 25 and modulus of approximately 840 kPa. A top plate is clamped under pressure as the silicone cures. The posts are bonded with a thin layer of silicone adhesive to the upper circuit layer to create a monolithic structure.
![](http://bdml.stanford.edu/uploads/Main/CapacitiveSensorDesign/armhfingernaked.jpg)
Flexible circuit for finger. Inset (upper left): detail of surface mounted IC
The same basic construction is used with flexible printed circuits for the fingers of the ARM-H hand:
![](http://bdml.stanford.edu/uploads/Main/CapacitiveSensorDesign/armhfingersensor.jpg)