Patent GB-715989-A (GB)
IPC: F16D71/04
Abstract: 715,989. Stopping shafts in predetermined positions. PHILIPS ELECTRICAL INDUSTRIES, Ltd. May 6, 1952 [May 9, 1951], No. 11437/52. Class 80 (2) [Also in Group XL (c)] Mechanism for positioning a shaft 8, e.g. for tuning radio capacitors and coils, of the kind wherein a selected one of a number of pivoted stop-pawls 46 grouped about the shaft is biased into engagement with a corresponding one of number of notched discs 36 frictionally clamped on the shaft, is provided additionally with a common pawl-release disc 57 having cam-shaped apertures 58 which, when the disc is turned through a limited angle, lifts any operative stoppawl and maintains all the others in a raised inoperative position, whereby the shaft 8 may be turned freely. For normal operation the shaft 8 is motor-driven through an overload release coupling carried on a parallel shaft 7, and becoming effective to break the drive connection and switch off the motor when a selected pawl 46 stops the shaft 8. Two such stop mechanisms are shown combined and geared together at a ratio other than 1 to 1 for stopping and positioning in a range of multiple revolutions, e.g. for adjusting sliding contacts of multi-turn coils, provided with means, not described, for automatically returning the adjusting member to the starting position. Overload release clutch. The drive enters at a gear-wheel 9, free on the shaft 7, to which wheel is secured the input ratchet-wheel 10 of the overload release clutch described in Specification 653,762 and comprising load sensitive tension-springs 14 between a final output gearwheel 12 and a floating intermediate member 13 which carries a pawl 19 and is prevented from backward movement (opposite to arrow P) by a roller ratchet 22 when the pawl 19 is lifted out of driving engagement with the input ratchet wheel 10, to break the drive connection, consequent on cam action between the intermediate and output members 13, 12, as the springs 14 yield on overload, the reaction member 16 of the roller ratchet 22 being permitted sufficient backward movement to open contacts 25, 26 in the motor circuit. The springs 14 then maintain a constant forward torque on the output wheel until the overload is passed. In this case the overload which breaks the drive is due to the positive stopping of the parallel shaft 8 by the stop-and-position pawls 46 of the stop mechanism. Positioning mechanism. A wheel 34, meshing the output wheel 12 of the overload release mechanism is secured on the shaft 8 to be positioned, on which shaft are frictionally mounted stop-discs 36, each having a single notch 37 for engagement with a corresponding one of the stop-pawls 46, which latter pivot in a freelymounted carrier 48, 49. The stop-discs 36, only two of which are shown here, are freely carried on rings 38 which alternate with friction discs 35 which are a force-fit on the knurled shaft surface and, are thin and flexible, so that when axial pressure is applied to the disc-pack through a clamping-screw 41, internal plunger 42, transverse key 43 in a slot in the shaft, and presser-plate 40, the flexible discs 35 and stop discs 36 are clamped against an end abutment plate 39 fast on the shaft. This method of mounting the discs is described in Specification 664,607. Pivot shafts 45 of the stop-pawls 46 have arms 47 with pins 50 projecting axially through the cam-apertures 58 of the common release-disc 57 to be on the periphery of a freely-mounted selector disc 51, which has a single recess 59 into which the pin 50 of a selected stop-pawl is pressed by a spring 56, carried by a gear-wheel 53 fast to the selectordisc 51, when the wheel and disc are turned to the appropriate angular setting. To prevent shock due to the sudden arrest of the shaft 8 by the stop pawls 46, the plates 48, 49 carrying the pawls each have a pair of spaced radial arms 61, 63 and 62, 64, which span a fixed frame post 5 with circumferential clearance which is taken up by a blade-spring 65 supported at its ends in the corresponding arms 63, 64 of the plates and pressing centrally on a cam 66 on the frame post 5, whereby the other arms 61, 62 of the plates are yieldingly pressed against. the frame post. When a stop-pawl 46 drops into a stop-disc notch 37, the stop-disc 36 and shaft 8, rotating in the direction R (the only direction), turns the pawl-carrier plate assembly 48, 49 in the same direction, thus flexing the spring 65 which cushions the stop and then returns the assembly to the initial position with the arms 61, 62 pressed against the frame post 5. Spring pressure can be adjusted by turning the cam 66. The common pawl-release disc 57 allows free selecting movement of the stop-pawls 46 in the position shown, but when turned in the direction of rotation R the inclined parts of the apertures 58 lift out of engagement any depressed pawl and hold all others raised, so that the shaft 8 can be turned freely by a knob 70 through reduction gear 71, 69. An alternative common control for turning the pawlrelease disc 57, axially meshing the wheel 69 and breaking the motor circuit, is by depressing a push-button plunger 305, Fig. 6, so that a diametral pin 309 rides in an axial slot 310 in a fixed guide-sleeve 302 and in a helical slot 311 in a freely-mounted bush 306, which latter is thereby turned and a toothed sector 312 on it turns the pawl-release disc 57, raising the stoppawls 46. At the same time the end of the plunger 305 breaks the motor circuit at 331, and a sleeve 317 surrounding the plunger is moved inwards through a spring 324 until its inner end contacts a shoulder 325 on the fixed guide-sleeve 302, at which time a toothed rim 321 on the sleeve 317 meshes the wheel 69, and the parts are locked in this axial relation by a spring- loaded ball 315 in the plunger entering a hole 334 in the fixed guide-sleeve 302. The shaft 8 can now be turned through the gear-pair 321, 69 by turning a hand-knob 320 on the sleeve 317. To return the parts to the original condition the hand-knob 320 is pulled outwards so that a coned recess 318 in the sleeve 317 presses inwards the lock-ball 315, thus freeing the plunger 305 for return outward movement by the spring 324. To permit drive from either end of the unit, the input wheel 9 of the overload release coupling meshes a wheel 67 free on the shaft 8, and the pawl selector wheel 53 meshes a wheel 30 free on the shaft 7. For stopping at selected points in a range comprising more than one revolution of the positioned shaft an overload release and positioning unit such as that shown (designated A) is connected by gearing with a positioning only unit (designated B), in Figs 2-5 (not shown). The pawl selector wheels 53 of both units are meshed together through an idler so that both units, which have the same number of pawls,. select simultaneously. The positioned shaft 8. of the first unit A is geared to that of the second unit B through a stepped wheel on the latter at a ratio such that the two positioned shafts: occupy their initial angular positions simultaneously only after a predetermined number of revolutions. In unit B the blade-spring cushioning means 65 for the pawl carrier 48, 49 is omitted, and the pawl carrier is pulled backwardly by a tension coil spring and is also flexibly geared to both its own common pawllifting disc and that 57 of unit A so that initially the pawls of unit B are permitted to select whilst those of unit A are all in the inoperative lifted position. Thus although selecting movements are made simultaneously in both units the selected pawl of unit B is free to engage its stop disc first, such engagement being followed by the pawl carrier in this unit being dragged forwards against the backward pull of its tension spring, which latter is weaker than the control spring 14 of the overload release coupling in the unit A so that drive is not interrupted. This forward movement of the pawl carrier of unit B causes a backward movement of the pawl-lift disc 57 of unit A, thus freeing the pawls of the latter. If now the notch of a stop disc 36 of the unit A does not immediately reach its selected pawl, the pin of the operative pawl of unit B rides out of the recess in its selector disc thus freeing the pawl carrier for return backward movement by the spring, which movement also lifts all the pawls of unit A to the inoperative position. The shafts of both units are thus free to continue in the forward direction of rotation and will be arrested only when the notch of a stop disc of unit A reaches its selected pawl at the same time as the selected pawl in unit B enters the notch of its stop-disc. This occurs only once in a range of a number of revolutions as determined by the gearratio between the positioned shafts 8 of the two units. Various additional interconnecting wheels permit drive connections from either side of the units.