GB975132A - Improvements in means for the production of variable electric resistances - Google Patents

Abstract

975,132. Making spiral resistance elements; coiling; winding. RELIANCE CONTROLS Ltd. April 28, 1961 [May 3, 1960], No. 15604/60. Headings B3A and B3E. A machine for winding a spiral resistance element comprises a coiling head for coiling an elongated flexible, insulating core into a spiral, a guide adapted to guide the elongated core through a winding head to the coiling head and having an outlet mouth adjacent the coiling head, the winding head being adapted to wind wire about the core as it passes from the outlet mouth of the guide to the coiling head, and means for moving the guide and winding head in dependence upon the progressive increase in the diameter of the spiral in such a manner that the mouth of the guide moves substantially along a line radial of the centre of the spiral and that the length of core tangential to the spiral and extending to the mouth of the guide subtends a substantially constant angle at the centre of the spiral. A strip 44 of insulating ribbon passes from a reel 43, through a tubular guide 41 mounted on a carriage 34, to be wound spirally on to an insulating boss 22 fitted on a rotating head 21. Resistance wire 47, from a braked reel 46 carried by a head 45 rotated about the guide 41, is coiled, by a pulley 48 on an arm 49 on the head 45, about the strip 44 as it issues from the guide 41 to the head 21. The head 45 may be provided with a revolution counter. Interleaved with the wire around strip 44 as it winds to spiral form on the head 21 is a slightly wider insulating strip 24 which passes from a reel 23 over a magnetic clutch 26, which serves to provide a progressively decreasing tension as the spiral grows, around rollers 28, 29, on an arm 30 pivoted at 32, to the head 21. As the diameter of the spiral increases, by bearing on the roll 29 the spiral moves the arm 30 about the pivot 32 and thus, through a roller 62 on the arm 30 engaging the carriage 34, moves the carriage and thus the guide 41 away from the centre of the head 21. As the diameter of the spiral increases the linear speed of the strip 44 increases, thus increasing the pitch of the wire 47 coiled thereon. The head 21 may be given an additional rotation to modify the pitch of the wire on the strip 44, by cam means, by moving axially a helical gear, engaging a gear 19 driving the head. Switch means may stop the machining after the required number of turns of the spiral has been wound. To wind identical potentiometers the speed of the head 21 may be varied, to apply correction, under control of a master potentiometer. Adhesive may be supplied to both sides of the strip 24 from tubes 83, 84. Specification 975,131 is referred to.