TakkTile

The world's most practical tactile sensor

Tactile sensors help robots grasp gently and correct errors before they knock objects over. However, to move outside elite research institutions, they need to be less expensive, more robust, and easier to manufacture than current options. TakkTile's breakthrough technology leverages MEMS barometers to deliver 1-gram sensitivity for a fraction of the cost of existing systems, in a package durable enough it can survive being crushed by a 25-lb weight.

    Making a sensor takes five steps:

    • Buy MEMS barometers and design a printed circuit board (PCB)
    • Solder barometers to PCB using standard industry practices or (on a budget) maker tricks
    • Design a mold that holds the sensors and restrains liquid urathane rubber
    • Pour rubber over barometers and vacuum degass them to bring the rubber into the sensors
    • Let cure and demold completed sensor

    On the electrical side, signals flow from barometers, to "traffic cop" microcontrollers (ATTINYs), to the main host (XMEGA).

    The barometer chips datasheet are hard-wired with a single I2C address. To circumvent the conflict this causes, a "traffic cop" microcontroller manages each group of 5 sensors by enabling/disabling a reset pin on the sensor packages. This allows up to 40 sensors (in the current implementation) to speak on the same I2C bus.

    The four-wire I2C bus is connected to either a commercial I2C to USB dongle (we use this one) or to a custom high-speed USB interface that reads at 100Hz.

    Plans and Source Code

    This is the alpha-release of the plans — they are provided as-is, with no implied warranty, but please download them, check them out, and let us know what you think at qwan_at_seas.harvard._edu and howe_at_seas.harvard._edu (remove underscores).

    Layout

    takkTile_overview.png

    Specifications

    • Array size - 5x8 sensors
    • Sensor spacing - 6mm
    • Weight - 11.6g (for the full board, which includes usb interface and programming pins)

    Design and Interface

    Eagle Files — use these to modify schematics, layout, and print PCBs using services such as seeed studio's fusion-pcb service. They were designed in Eagle 6.0.0—if you run into problems opening the files, check your version. Sparkfun.com has some great tutorials on how to use the software. A few notes are listed here

    Firmware files — use these to program the addressing microchips on the tactile arrays, and the microcontroller on the host USB board.

    Plastics — we cast the sensors under 6mm of Vytaflex 20 from Smoothon Polymers, Inc. Degassing after pouring over the barometers is extremely important to maintain sensitivity (you can use a standard vacuum pump at roughly -760mm Hg for about 5 minutes).