Patent GB-847488-A (GB)
Title: An improved gear measuring apparatus
Filed: 1956-09-18
Abstract: 847,488. Measuring gear errors. HOFLER, W. Sept. 18, 1956 [Sept. 21, 1955], No. 28471/56. Class 40 (1). An automatically operating gear - testing apparatus for measuring tooth errors of continuously moving gears and gear-like test objects has a slide adapted to be reciprocated periodically towards and away from the test object, a pivotable measuring feeler or a plurality of feelers carried by the slide, means for returning the feeler or feelers during the retraction of the slide, control means operated in response to pivotal movement of the feeler or feelers to control the advance and retraction of the slide by means of a rotatable electric motor and an electrical measuring system operatively connected to the feeler or feelers to evaluate or record the movement thereof. As shown in Fig. 1, a slide 41 is mounted by means of rollers on a base 40 and is moved towards and away from a gear 46 to be measured by a motor 47 which reciprocates the slide 41 through a rack 49 and a pinion 48. Connected to the slide 41 by means of leaf-springs 43 and 44 is a measuring slide 42 the leaf-springs permitting it to move independently of the slide 41 towards and away from the gear 46. The slide 42 pivotally mounts a feeler 45 the free end of which engages the gear 46. As shown, the free end is a gear sector 45<SP>11</SP> but alternatively a ball or a single tooth can be used. Also carried by the slide 42 is one electrode 54 of a condenser the other electrode 55 of which is carried by the slide 41. In use the slide 41 is moved towards the gear 46 by the motor 47 until the slide 41 engages a stop ledge 53 on the base 40; when the slide stops moving the rack 49 continues to move against the pressure of a spring 52 which is interposed between it and the slide and this movement breaks the motor circuit through a contactbreaker 51 mounted between the slide and the rack. During this movement of the slide 41 the feeler is biased to the right against a set-screw 61 by a lever 57 and a spring 60 and when the end of the feeler engages the gear 46, which is assumed to be in continuous rotation in a clockwise direction, it is pivoted by this rotation anticlockwise. This movement of the feeler 45 moves the slide 42 relative to the slide 41 and consequently changes the capacity of the condenser formed by the electrodes 54, 55. After the slide 42 has moved to its maximum extent the contacts of a switch 50 mounted between the feeler and the slide 41 make and operate a contactor which controls the motor 47 so that it then proceeds to retract the slide 41 away from the gear 46; the initial movement of the rack 49 causes the contact-breaker 51 to make but the circuit through this contactbreaker is broken by the contactor controlled by switch 50. The retraction of the slide 41 and hence of the slide 42 eventually brings one end of the lever 57 into engagement with a stop member 56 carried by the base 40 and pivots this lever; once the pivoting movement starts it is completed by the spring 60 and since the other end of the lever 57 is connected to the feeler 45 the feeler is pivoted clockwise to its initial position against the setscrew 61. This pivoting movement of the feeler causes the contacts of switch 50 to separate and thus the contactor is released, the release making the circuit through the circuit-breaker 51 so that the motor reverses and advances the two slides towards the gear 46 so that the feeler can engage its teeth. The condenser 54, 55 controls the frequency of an oscillator a, Fig. 5, and this frequency is applied to a mixing circuit c where it is mixed with a fixed frequency from an oscillator b. The beat frequency from the mixing circuit c after amplification is converted to. a D.C. voltage in a circuit e the amplitude of which is proportional to the frequency and this voltage is applied to a recorder g. For each measurement a single peak curve is recorded, the peak value of which depends upon the gap between adjacent teeth; deviations of adjacent peak values relative to each other indicate tooth spacing and pitch errors and deviations of peak values within a series indicate errors in concentricity of the teeth. In an alternative embodiment, Fig. 7, for determining tooth spacing errors, two pivoted feelers 80 and 81 are used these engaging the corresponding faces of adjacent teeth. Each feeler is pivotally mounted on a separate slide 91, 92 the slides being carried by a slide 86 so that they can move transversely of the slide 86; their relative position is adjusted by threaded spindles 93, 94 and they are locked in a desired position by set-screws 95, 96. The feelers are maintained in contact with the tooth spaces by springs 103, 104. The slide 86 is mounted on rollers on a base 84 and is moved towards and away from a gear 83 which is to be measured by a motor 87 which moves the slide through a pinion 89 and a rack 88. In use when the slide 86 is advancing towards the gear 83 the feelers 80, 81 are biased to the left, as shown in the drawing, by the springs 103, 104. When the slide 86 is stopped by engagement with a ledge 90 on the base 84 the motor is stopped by the opening of a contact breaker 109 between the rack and the slide 86 as in the previous embodiment and the tips of the feelers enter between the teeth of the gear 83 which is assumed to be continuously moving anticlockwise. The feelers are rotated clockwise by the engagement with the gear and their movements change the capacity of condensers connected between the feeler and the slides 91, 92. The condenser between the feeler 81 and the slide 92 controls the frequency of an oscillator A, Fig. 9, and this frequency is mixed with the frequency from a fixed frequency oscillator C in a mixing circuit B. The beat frequency is amplified and converted in a circuit E to a D.C. voltage the amplitude of which depends upon the frequency. When the amplitude reaches a predetermined value it causes a relay R to operate and this relay connects the D.C. voltage produced by a circuit E<SP>1</SP> to a registering instrument F and a recording instrument G. The amplitude of the voltage from the circuit E<SP>1</SP> depends upon the capacity of the condenser between the feeler 80 and the slide 91 since the condenser controls the frequency of an oscillator A<SP>1</SP> which is mixed with the fixed frequency from an oscillator C<SP>1</SP> in a circuit B<SP>1</SP> the beat frequency being amplified and applied to the circuit E<SP>1</SP> to produce the D.C. voltage. The voltage registered and recorded is indicative of the measurement required since the relay R operates at a predetermined voltage and hence at a predetermined position of the feeler 81. At the same time as the relay R is energized a relay R<SP>1</SP> is also energized but the closure of its contacts 106 is delayed for a short period. When the 'contacts 106 close a contactor R<SP>11</SP> is energized and its contacts complete the circuit for the motor 87 so that it retracts the slide 86 and also breaks the circuit through the contact breaker 109. The relay R<SP>1</SP> is arranged to release its contacts 106 after a short period and when this happens the contactor R<SP>11</SP> releases and the circuit through the contact breaker 109 is made so that the slide is again advanced towards the gear 83.