Tactile Sensor Construction Technology

Our lab has been using capacitive sensor technology since 1984. The interface circuit we are using has been designed by Matt Berkemeier, Ed Nicolson and Ron Fearing. The technology is based on earlier work by:
R. A. Boie, ``Capacitive Impedance Readout Tactile Image Sensor,'' IEEE Int. Conf. on Robotics and Automation, Atlanta, GA, March, 1984.
Boie, R.A. and Miller, G.L. 1985. Conformable tactile sensor. U.S. Patent #4,526,043.
D.M. Siegel, I. Garabieta, J.M. Hollerbach, `` A Capacitive Based Tactile Sensor,'' SPIE Conf. on Intelligent Robots and Computer Vision, Cambridge, MA Sept. 1985. The capacitive tactile sensor developed by R. Fearing at Stanford University has 7x8 elements on the cylinder and 8 elements under the hemispherical tip.

The sensor design and behavior is described here:
R.S. Fearing, ``Tactile Sensing Mechanisms'', Int. Journal of Robotics Research , vol. 9, no. 3, June 1990. link
doi: 10.1177/027836499000900301

See Ed Nicolson's PhD Thesis for some detailed specs.

Tactile Sensing and Control of a Planar Manipulator in pdf

E. Nicolson

Ph.D. Thesis, University of California at Berkeley, November 1994.

We would like to see other people able to use the technology, so we are making our schematics available. All parts except for the HI5320 S/H are readily available from DigiKey. There is also a detailed set of instructions on constructing a tactile sensor using silicone rubber.

Summary of electronic specifications:

8 by 8 sensors (16 by 16 in progress)
200 frames per second
capacitance resolution of 100 attofarad (10^-16 Farad) at 200 Hz
Schematic of Scanning Clock Circuit
Schematic of Timing Clock Circuit
Schematic of Demodulator Circuit
(.ps) Schematic of Charge Amplifier Circuit (.pdf)

Summary of sensor specifications:

The figure shows a 16 by 3 sensor designed by Ed Nicolson and Kiwoon Kim. We have built sensors ranging from 16x3 on 25 mm diameter to 8 by 8 on 1 mm by 1 mm. For the 25 mm diameter sensor we have:

7 bits resolution
2% of full scale hysteresis after 1 second
noise s.d. of 0.05% strain, linear to 10% strain
Notes on fabrication of cylindrical tactile sensor. (pdf)

Future Directions

Improved tactile finger construction techniques to allow a more uniform sensor response.

Papers

A Surface Micromachined Microtactile Sensor Array
B.L. Gray and R.S. Fearing
IEEE Int. Conf. Robotics and Automation, April 1996.

Sensing Capabilities of Linear Elastic Cylindrical Fingers,
E. Nicolson and R. Fearing,
In Proceedings, IEEE/RSJ International Conference on Intelligent Robots and Systems'93,
Yokohama, Japan, pp. 178-185, July 1993.

The Reliability of Curvature Estimates from Linear Elastic Tactile Sensors,
E. Nicolson and R. Fearing,
Presented at the 1995 IEEE International Conference on Robotics and Automation,
Nagoya, Japan, May 1995

Fourier Analysis of the Bandlimited Shape Estimation Problem in Tactile Sensing,
E. Nicolson and R. Fearing,
Internal Memo, October 1994

Tactile Sensing and Control of a Planar Manipulator in pdf
E. Nicolson
Ph.D. Thesis, University of California at Berkeley, November 1994.

See also:

"Basic Solid Mechanics for Tactile Sensing,"
R.S. Fearing and J.M. Hollerbach,
Int. Journal of Robotics Research, vol. 4, number 3, Fall, 1985, pp. 40-54

"Tactile Sensing Mechanisms,"
R. S. Fearing,
Int. Journal of Robotics Research, vol. 9, number 3, June, 1990, pp. 3-23

Ed Nicolson's home page

Last update: 11 August 1995