Contact Shape Sensor Prototype
The images below demonstrate a thin flexible contact shape digitizing technology described in US Patent 5563458. For more details go to bistabledome.org and tactile digital bend and shape sensor . Also see: single row shape sensor prototype videos for single sensor demonstation of unique 2D profile and bend digitizing capabilities.
Five parallel bistable dome sensor strips, each strip consisting of 25 flex-actuated overlapping bistable dome switches, are used to digitize shape and changing shape. Unlike tactile domes, flex-actuated bistable domes are switched by flexure of their edges or the material attached their edges, not by direct pressure to the dome. Overlapping flex-actuated bistable domes share the flexural forces that switch individual domes and are free to switch back and forth in the sensor. The domes switch to neutralize local flexural forces in patterns that indicate where, how much, and which direction from flat the sensor is bent. Each sensor can provide unique 2D profile information.
In this large scale, low resolution demonstration there are approximately four domes per inch, each wired to a corresponding LED. The sensors are approximately .06" thick. Visible wiring would be eliminated in final product. The following images show various objects and shapes sensed in different orientations and pressures. Description of sensor continues at bottom.
Below: Sensor can tell between disc shapes of different diameter, in different places on sensor. Center hole of first disc shape is too small for this resolution so it is treated as flat. Hole in roll of tape is large enough to be sensed since the sensor can maintain some of it's original convexity through the hole.
Below: Sensor senses flatness of side of wood but resolution too low and it's not flexible enough to sense flatness of edge. Lines are well defined, however. With a better constructed, higher resolution sensor LEDs under the flat sides would register as half on and half off.
Below: Changing patterns caused by deformation could be used for analyzing angle of sensor relative to flat floor or wall- for automated leveling, navigation, smart tires, bumpers, etc.
Below: Radius only slightly greater in second image but position is different and pressure probably greater in second. In third image lower density of lit LEDs corresponds to larger radius.
Below: Sensor is flexible and sensitive enough for sponge. Flexible sponge edges not as straight as wood edges.
Below: Sensor digitizes position and increasing pressure with small radius flashlight.
Below: Possibilities for human computer interface.
Below: Selected images from fist indentation continuum from 0 to 33.
Sensor reaction to flexure is very predictable. For many applications only relative measurement may be necessary. Adding sensors to form a grid or net could improve 3D information significantly. Resolution is determined by the diameter/density of domes.
Each sensor strip is a row of bistable domes formed in thin steel and sandwitched between two layers of thin flexible polycarbonate. A copper tape strip is used as a contact opposite and on one side of each dome. Layers of tape are used to provide proper spacing to contain the dome row along it's edges while giving individual domes the space to switch.
When a dome top contacts its corresponding copper strip it completes a circuit wired to a corresponding LED. The LEDs are aranged in five rows and are spaced very similarly to the actual switch spacing.
The five sensor strips are taped to five parallel flexible polycarbonate strips. When no force is applied the sensors are forced to return to identical convex resting positions at which all switches are off. Starting profile does not have to be convex- it could be flat or alternately contoured.
Such sensors may be miniaturized and mass produced with common metal stamping and flexible circuitry technology to increase resolution, reduce minimum radius limits, and minimize wiring. Using flexible circuitry the wiring used in each sensor of this prototype could be reduced to a paper thin tape less than .15 inch wide. The final sensor might look like a plastic wire tie with a connecting plug and the wiring included along its length.
For more information and application suggestions see Tactile digital bend and shape sensor. Sensor design for flexible circuitry available.
See : single row shape sensor prototype videos.
Contact: Paul Ericson
barkingpo at earthlink.net
PO Box 576
Cerrillos, NM 87010
US Patent # 5563458. Apparatus and Method For Sensing Surface Flexure (Note: use new contact address above).