Integrated Wiring

If we wish to include distally located sensors on our robotic mechanisms, we need a method for intregrating the wiring in the structure, particularly over joints, to safely attach the sensors to the control electronics and power without infering with the motion of the robot.  A method that we have investigated for doing this is described below.

Producing the wiring ribbon cable

close-up of ribbon cable
Close-up of wiring ribbon cable

solder tinned ribbon cable
Close-up of the ribbon cable tinned with low melting point solder

Step 1:  Pattern copper (or gold) foil that is attached to non sticky back Gel-pak 8 with the laser.  We, for instance, pattern the copper foil such that we have three wires that are each 400 µm wide with 150 µm spacing between them.
Step 2:  Remove excess foil and spin coat a thin layer of polyimide (PI 2525) on the patterned foil.
Step 3:  Place a sheet of 7 micron thick Kapton® over the spin coated polyimide.
Step 4:  Heat on a 300 deg C hotplate for 5 minutes.  Remove the Gel-pak and heat wiring with Kapton® backing for a remaining 20 to 25 minutes.
Scheme for integrating the wiring in the parts and over flexure joints

schematic of integrated wiring

The wiring ribbon cable is included on the link elements.  Where necessary, a loop of ribbon cable is placed over the joints.

The electrical connection is made through the use of low melting point solder (e.g. TIX soft solder). The ends of the ribbon cable on the link elements as well as the ends of the loops of ribbon cable placed over the flexure joints are tinned with the low melting point solder. 

An application of heat (for example, with a soldering iron) on the ribbon cable ends where it overlaps between the flexure joints and links will electrically connect the two together.

Example structure with use of wiring

Schematic of a crawling robot with 4-bar legs that senses surface contact

example of use of wiring on a crawling robot
Actual structure that was built (one 4-bar leg) in a test setup

4-bar leg in test setup with close up of wiring

Sample test result

strain gage data from foot hitting a surface

The first graph compares the strain gage data obtained using the integrated wiring with the input signal that we were supplying to the actuator.  (We supplied a sinusodial input so that the foot would repeatedly "kick" the steel surface.)  Note that one can tell clearly when during the cycle the foot was making contact with the surface.  The bottom graph shows the difference in signal as the amplitude to the actuator signal was increased.  The data correctly records the increase in force with which the foot was hitting the surface.