GB498030A - Improvements in gramophones - Google Patents

Abstract

498,030. Gramophones. DEHN, F. B. (Automatic Musical Instrument Co. ) March 24, 1937, No. 8682. [Class 40 (ii)] Relates to devices for controlling a motor which effects the lifting of the pick-up arm of a gramophone after the playing of a record and its return to the starting position. According to the invention, the pick-up arm 10 carries a slide 36 for actuating a switch 41 mounted in the path of the arm and adapted to control means for moving the arm to the starting position, the slide being advanced towards the switch, by means carried by the arm, when at the end of the playing of a record the needle imparts rapid inward movement to the arm or oscillates it by entering an eccentric groove. The switch may, as shown, comprise electric contacts, or may be a mechanical trip device. In the machine shown, a motor 27 is geared to a shaft carrying a cam drum 26 having at one end a flange 25 with a flat portion 30, and having in its surface a groove which is partly semicircular and partly spiral, the latter portion leading to an enlarged portion 29. A pin 28 engaging in the groove is carried by a bracket. 24 extending from the base of the pick-up arm. The bracket carries a plate 33 which overlies a platform 31, and is also provided with lugs 34 which engage in triangular apertures 35 in the slide 36. The slide has ratchet teeth 38, and a gravity pawl 35a is pivoted on the plate 33. When the pick-up arm is in the position of rest, Fig. 2, the bracket 24 engages the high portion of the flange 25, and the slide 36 is suspended on the lugs 34. When the motor 27 is switched on, manually or otherwise, the drum 26 is rotated clockwise until the flat part 30 of the flange allows the pick-up arm to descend after the.spiral part of the cam groove has, by acting on the pin 28, moved the arm 10 inwards so that the needle is over the beginning of the sound groove. The motor 27 is then switched off by suitable means (not shown), and playing begins, the pin 28 moving in the enlarged part 29 of the cam groove. The slide 36 is at this time held up by the platform 31, with the pawl 35a engaging the ratchet teeth 38. At the end of the record, the slide is advanced until a screw 40 thereon closes the switch 41, the forward movement being sudden, when the record has a quick run-off groove leading to a concentric terminal groove, or step by step through the action of the pawl 35a if the terminating groove is an eccentric one. Closure of the switch 41 starts the motor 27 to turn the cam drum reversely and to effect the lifting of the pick-up arm and its return to the starting position. In a modification, the slide 36 has a second set of ratchet teeth coacting with a holding pawl, and a retracting spring is provided.