Abstract: Armature (4) is driven by piezo-electric vibration elements (1) which are made to resonate by means of high-frequency electrical oscillations in order to produce ultrasonic vibrations which are transmitted to a plurality of drive pins (2) arranged as brushes a friction surface (6) of the armature (4) is pressed against free ends (5) a of the pins, the individual drive pins bein disposed at an angle .alpha. relative to the perpendicular to the contact portion of the friction surface (6). The angle of inclination .alpha. is then substantially equal to the static-friction angle or is slightly larger than this static-friction angle between the drive pins and the friction surface. Suitably, the angle of inclination is selected to be between 10.degree. and 30.degree..

Abstract: A device for positioning an optical fiber with respect to a defined reference plane. The optical fiber is arranged so as to be displaceable with respect to the reference plane by an electro-mechanical deflector device comprising three pairs of deflector elements which are arranged like parallel leaf springs.

Abstract: A projection television display tube having an evacuated envelope (1) with a display window (4) which has a display screen (5) on its inside and in front of which a light-permeable second window (6) is provided on the outside, a cooling liquid flowing through the space (7) between the display window (4) and the second window (6) from at least one inlet aperture to at least one outlet aperture. When in such a projection television display tube a cooling jacket(8) is provided at the area of the windows (4, 6) and around the said space (7) and is provided with at least one duct (9) and one pump (16) with connecting nipples (17,18) which transport the cooling liquid from the outlet aperture to the inlet aperture or apertures of the said space (7), an effective cooling is obtained with a power up to 40 W without outer pipes and without heat exchangers. By the forced circulation of the cooling liquid a good temperature compensation is obtained so that fewer stresses occur in the glass of the display window.

Abstract: A surface testing apparatus includes a bilaminar ceramic flexure element provided with means for generating a voltage which is proportional to the deflection of the flexure element. This voltage is compared with a reference voltage. After amplification the difference voltage is applied to the flexure element so that the applied force remains constant, independently of the deflection.