| 摘要 |
1,187,823. Adjusting devices. CTS CORP. 19 April, 1967 [20 April, 1966], No. 18042/67. Heading H3Q. [Also in Divisions F2 and H1] A variable resistance unit has a slipping coupling for preventing relative movement of the two parts beyond a predetermined point, the coupling comprising a driven member having a rim part of which can flex to interrupt the connection between the driving and driven members. Fig. 3 is an exploded view of a variable resistance unit containing a resistance track 44, sliding member 60 and gear-wheel 20. The latter is driven by a worm-wheel 31 (Fig. 5) formed integrally with a screw head 34 which projects out of the back of the unit (Fig. 1, not shown); the worm is prevented from moving axially by a groove 33 into which projects a nylon pin 32 (Fig. 3) sufficiently tightly to secure the worm against vibration or shock. The gear-wheel 20 is preferably of insulating material such as nylon or polyfluorodichloroethylene; if of metal, the worm should be of insulating material. Rotation of the gear-wheel is communicated to the resistance slider 60 by means of pins 28 which are a force-fit in a hole 62 and opening 61 in the slider. The lower side of the gear 20 has an annular portion (26 in Fig. 4, not shown) of reduced thickness separating the hub of the wheel from the rim. This annular portion is interrupted by a short section (27) of the full thickness of the gear, and when the gear has rotated sufficiently for the slider 60 to reach the end of the resistance track this section (27) abuts against a projection 18. On the other side of the gear the reduction in thickness is carried through to form an arcuate slot 29. If the worm continues to rotate after the section (27) has reached the stop 18, the rim of the gear adjacent the slot 29 will flex inwardly and disengage the teeth from the worm, preventing damage to the resistance unit. It may not be necessary for the slot 29 to extend through the full thickness of the gear. In an alternative form (Fig. 6, not shown) the slot 29 is divided into two parts each of which reach the edge of the gear so that a portion of the toothed rim forms a separate segment. The gaps are small enough to permit continuous engagement of the gear with the worm. Resistance track (Fig. 3).-This comprises a ceramic film 44 fired on to an alumina or steatite substrate 42 as in Specification 1,091,916, or alternatively a carbon track or wire-wound element. Contactor 64a wipes the track while contactor 65 rotates on a centre collector 45. L-shaped leads 49 enter holes 47 in conductive pads 51 at the ends of the track and are fastened thereto by a conductive epoxy resin. A lead 50 is similarly attached to the centre collector at 48. The leads are fastened to the substrate by an insulating epoxy resin (53 in Fig. 1, not shown). The whole unit is enclosed in a housing 11 of diallyl phthalate resin or die-cast aluminium. The substrate 44 rests on a ledge (12b in Fig. 2, not shown) and the annular gap round the edge of the substrate is filled with adhesive (56). |
