patent on a new version of IBM’s electrostatic clutch using the #Johnsen-Rahbek effect in 1979. #patents
on 02015-11-26Development of the Electrostatic Clutch: “A brief historical review of the electrostatic clutch operating on the #Johnsen-Rahbek effect is presented. #Mechanical design of a clutch, special lubrication, and the fabrication of electronically conductive clutch facing material are described. A high-speed, high torque-to-inertia ratio test model with bi-directional shaft control is described. With the clutch operating at 2500 rpm on 30 milliamperes at 150 volts, torques over 80 inch-pounds are available. The most useful single property of the electrostatic clutch is its fast response time. It can actuate levers, interposers, print hammers, optical gates, etc., in fractions of a millisecond; it can accelerate shafts to high rpm’s with moderate loads in a few milliseconds from extremely low input control energy.” Fitch 1957. Note that 30mA×150V is 4.5W, while 80 inch-pounds × 2500 rpm is 2400 W, an amplification factor of >500.
on 02015-11-26John Nagle mentions Edison’s “chalk telephone”, which used the #Johnsen-Rahbek effect to directly control friction between a rotating damp chalk cylinder and a wiper. “Silicon carbide was much better than wet chalk, and this effect was used in IBM line printer clutches.” Perhaps this could be used for controlling a 3-D printer. #materials
on 02015-11-26