An experimental crystal clutch recently developed at the National Bureau of Standards is believed to be the first of its type. In the new clutch, application of a direct-current voltage to the electrodes of three "Bimorph TM piezoelectric crystal elements causes bending of the elements; this bending presses the clutch output disk against the rotating input disk. The new experimental unit was devised by Ernest Codier of the NBS staff as part of a program for the development of fast-acting clutches suitable for use in high-speed computers.
Distinguishing features of the crystal clutch are high speed of response and almost negligible current drain. No current flows, other than insulation leakage, after the applied voltage has charged the capacity of the crystals. The clutch therefore creates no magnetic field, an advantage in some applications.
In the only clutch model thus far constructed, the output shaft delivered useful torque in as little as 0.2 millisecond after voltage was applied. Output torque of the engaged clutch was approximately 16.5 ounce-inches at 400 volts excitation, or 21 ounce-inches for 500 volts. The no-voltage drag torque, however, was about 7.5 ounce-inches, a substantial fraction of the engaged torque.
Construction of the crystal clutch is essentially simple. The output disk is located between two rotating members: a thin, flexible crystal pressure plate and a heavier mounting plate or input disk. Three of the Bimorph crystal elements, which bend when opposite potentials are applied to different parts of the crystal surfaces, are spaced at 120-deg. intervals. When the exciting voltage is applied, the crystals press against the pressure plate at a radius of 1.5 in., pinching the output disk between the pressure plate and the input disk.
The clutch proper and its immediate mounting occupy a space about six inches in diameter and a little more than an inch long. The complete assembly includes, in addition, internal bearings for the output shaft, bearings and mounts for the entire assembly, a drive pulley, and slip rings for transmitting the exciting voltage to the rotating assembly.
The new clutch was tested for speed of response by placing the needle of an ordinary crystal phonograph pickup in a small dimple in the clutch output shaft. By connecting the pickup output to the * Communicated by the Director.
Product of Brush Development Company.