US2204065A - Motor driven tuning system - Google Patents

Description

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NUON" m. u H. M W H H. H. BEIZER ET AL.

MOTOR DRIVEN TUNING SYSTEM Filed June 1v, 195s June 11,1940.

Patented June 11,1940

UNIT-ED STATES PATENT *l OFFICE MOTOR DRIVEN TUNING SYSTEM Application June 17, 193s, serial No. 214,390 4 claimV (o1. 17a-zas) The present invention relates to an electric motor control system particularly adapted for tuning control of radio receiving apparatus and the like, wherein a, reversible ,electric motor is connected to drive a radio tuning device under control of circuit elements for causing the motor to move the tuning means from one to another of several preselected tuning positions.4

Motor tuning for radio receiving systems providing for remote control tuning and preselection tuning' has gone into more extended commercial use with the advent ci recent automatic freouency control circuits which, as is' known, permit the oscillator frequency to ice adjusted cutolli motcolly to correct for inaccuracies in tuning adjustment in a superheterodyne receiver.

utoniatic frequency control circuits ,toev corncertain receiving systems and edd to if cost reore than desirohle. However, acci o' tuning is importent, itis e, primary of the ove ent invention to provide c :cotos f qe particularly to e,

isle motor sv om in which the mon tor circuit is opened to lering' i Vine' system to rest e. preselected position when eiectricei contact ou reversing con'iinutotcr device, connected with. the tuning control sho-it, reaches insulati segment 'between tivo refversing discs or segments of the comrnutotor de vice.

i5 The accuracy of stopping depends upon the vv' oi the insulator or segment and the rod-ius ci the oommutetor device at the segment and is preferably such that the tuning syst/ern may stop for accurate tuning adjustment towithin one c. or' the desired signal frequency.

The matter of speed in tuning is also important and with accurate stopping, the necessity for higher speed in tuning may cause over-travel ci the motor at the insulating segment and reversed of the motor and the tuning'. Although the overtravei may ce small in amount, even with an' armature of low inertia in the motor, it has been. difficult heretofore to control the stopping for accurate tuning without oscillation or hunting.

It is therefore a further 'object of the present i invention to provide a reversib'le motor tuning system for radio receivers which may provide rel-4 atively high speed tuning movement while at the -same time providing accurate tuning adjustment 55 without hunting or oscillation about the stopping point, whereby the necessity for automatic frequency control circuits, and the like, may be eliminated. O

It is a still further object, of the present invention to provide an improved reversible motor tuning control system for radio receiving apparatus, and the like, which eiectively utilizes the reversing action of the motor means to provide accurate tuning adjustment to preselected tuning pol sitions.

It is an object of the invention, furthermore, to provide a reversible motor tuning control system 'for radio receivers, and the like, having a reversing commutator device in which the insulating geo or segment of the device between the revers@ ing segments may loe ricade relatively narrow for accurate tuning, vfhileat the same time providing high tuning movement lov the motor means, without oscillation or hunting about the stopping positions The invention will, however, he better vendere stood 'from the following description when cori-T4 sidered in coieoection with the accompanying drawing and its scope will he pointed out the appended cleiins.

f in the drovvins Figure i e. sclieniotic circuit 'divorcio tofgether with a diagrammatic Tfepresestation or" e. tuning system for a receiver, embodying the invention, and

Figure end view of e, mechanical detail. the system showoin l, and en lsreecl sco-ie.

Referring to the drawing, a, tuning system for o radio receiver or like apparatus is diagrommoti call-f; represented by usual threesome vari laisle tuning capacitor, indicated at having* a tuning controlsiiait Ei coupled through a shaft l to o cord drive Wheel or drum 3, and at the op'- posite end through a shaft Q to a reversing comm mutator device iii comprising two reversing contact segments ii and i2 and an insulating gap or segment i3 therebetween. The vsegments il and i2 are connected through reversing leads M, respectivelywith reversing windings i5 and i6 of a reversible electric motor il.

The motor is 'energized from a suitable source oi low voltage alternating current, such as a sec ondary winding i8, on the power transformer i9 of the radio receiver. One side of the secondary l is connected through a lead 20 with avmain operating winding 2| oi' the motor, while the opposite side of the secondary is connected through a lead'22 and a series of push-button selector switches 23-2'l, inclusive, selectively with one that the switches 22-2I, inclusive, are connected in series when in the open position and the series circuit is completed to the potential supply lead 22 through the contacts of a multiple ccntact switch 2l. This series circuit arrangement prevents more than one selector button from becoming effective to operate the motor, thereby preventing overheating of themotor should it receive operating turrent continuously through more than one selector switch and both reversing windings at'the same time.

The motor circuit arrangement issuch that while the contact 20 is over the insulating gap or segment 'the motor circuit is opened and the motor is deenergized following closing of the switch 25. The contact I0 when closed with the segment II energizes the reversing winding I6, causing the motor to drive the tuning shaft I and the commutator device Il through a gearing connection hereinafter described, in a 'direction to restore the commutator to the position shown, with the contact 30 at the gap I2. Contact with the segment I2 causes a similar movement in the opposite direction to restore the commutator to the position shown. Thus the tuning is always brought to the same point of rest for each selector switch. l

l The contacts 28-32, inclusive, are movable or adjustable with respect to the insulating gap or segment ,I3 to cause the radio tuning device to stop in any one of a plurality of preselected positions corresponding to desired signals or radio stations to be received. In order to provide a high degree of accuracy in tuning, the segment Il or insulating space between the reversing segments II and I2 must be relatively narrow as are also the contacts 28 to 32.

In a present preferred embodiment of the invention the insulating segment I3 is provided at the periphery of two hat metal plates, in the form shown at II and I2, mounted to rotate in connection with selector contacts 2l to 32, inclusive, located at a distance from the center of rotation of from three to four inches, whereby a small degree of angular rotation provides a relatively wide range of movement for the insulating gap.

With'this arrangement the width of the insulator or gap. has been set at 0.75" and the diameter of the contacts has been set at .059"A which permits .008" on either side of each contact when it is centered on the insulator i'or` an exactly tuned-in positionl of the tuning device.

It has been found that with a relatively small amount of over-travel with an ordinary motor drive and with production tolerances in the insulating gap varying from the values above given, and even when the motor armature has relatively low inertia, it is ldifficult to control the tuning without excessive oscillation or hunting about the stopping point.

However, the accurate adjustment providedl bythe narrow insulating gap in the reversing commutator may be maintained and accurate stopping may be provided without oscillation'or huntingif the driving motor is further controlled as will hereinafter appear.

The motor is of the shifting armature type, having anv armature 2l mounted on a shaft l! and axially movable therewith`when energized, against a spring 40 to cause a crank arm II carried by the shaft to engage between the teeth I2 (Fig. 2) of a star wheel l2 which is mounted on a driving pinion 44. The pinion M forms part of a. gear train "-48 connecting the star wheel 43 with a tuning control shaft 41 for manual tuning and having a suitable tuning control knob The shaft ,l1 is connected with the drum 8 through a, cord drive indicated at 4S, and a similar cord drive indicated at 50. is also connected with the drum or sheave 8 to actuate a. tuning dial pointer or indicator 5I, in

' connection with a tuning indicator dial shown When the motor amature is energized the crank arm il engages the star wheel l2 by means of the crank pin and drives the gear train l4l-li which in t-urn drives the tuning control shaft The tuning control shaft is connected to the variable tuning vdevice 5 through the cord drive which provides a reduction ratio of 17:1, for example. The reduction ratio from the motor shaft to the tuning control shaft l1 may be substantially`25z1. With this reduction and a. present available type of motor, the time required to tune from one end of the broadcast band to the other is approximately three seconds. When lthe motor is deenergized the armature is thrown clear of the star wheel and pinion by means of the spring 4I, the armature itself having axial. movement, as hereinafter referred to. t

A flywheel 6l mounted on therrear end of the motor shaft 29 between stop washers indicated at 6I is free to rotate on the shaft but is prevented from axial movement with respect to the shaft by the washers. The flywheel provides an inertia weight or device for imparting axial and rotational inertia to the drive system and preferably, as shown, to the motor shaft.

Driving torque is transmitted to -theflywheel from the shaft through a friction plug indicated at I2 in a radial recess Il in the fiywheel. The plug is pressed against the shaft by a suitable spring 6l. Ihe friction plug may be of leather and the pressure on the shaft is controlled by the screw 05. The action of this ywheel controls the over-travel of the motor and the accuracy in the direction of the corresponding station or I selector contact such as the contact 3L Ihe motor cannot come up to speed immediately because of the friction load of the slipping flywheel which provides a momentary overload but does so as soon as the inertia of the flywheell is overcome.

W'hen the insulator I! on the selector disk reaches the station contact 3l, for example, both the motor and nywheel are rotating at the same speed and the combined inertia carries the tuning mechanism and the insulating segment past the'stop position and the contact 2l, thereby causing the motor to reverse. Because of the momentum of the flywheel l which is still rotating in the original direction, and the friction between the ywheel and the shaft, the motor speed in reverse is reduced.

f While the Imotr is rotating at low speed in the `hold the armature in the forward position and to maintain the crank arm in engagement with the star wheel during this brief interruption, thereby preventing declutching and lost motion y in the reverse driving action of the motor.

Adjustment of the set screw 65 on the flywheel friction pad controls the amount of over-travel and the accuracy of tuning. In order to ensure that the motor may provide final tuning while rotating very slowly, the drive pinion 4l has been provided with a multiple bladed star wheel, as shown in Fig. 2, which permits the motor to start Areversing the tuning shaft immediately before the motor attains speed, which would cause the selector to over-travel the selected contact and hunt or oscillate.

With the reversible motor tuningvsystem described, it will be seen that the reversing commutator may be provided with a relatively narrow insulating segment between the reversing disks or ksegments and on a relatively long radius providing accurate stopping and eliminating the necessity for automatic frequency control nf the oscillator.

Furthermore, the tuning system may be made to operate at a relatively high speed, that is, it may have a relatively high rate of tuning movement, together with accurate stopping with the commutator device above referred to, by providling the ytuning motor with a flywheel frictinallyi` connected with a shaft driven by the motor, preferably the motor shaft itself, as shown, which applies a rotary braking effect to the motor when the latter is reversed. The friction between the iiywheel and the shaft is adjustable and starts the flywheel spinning in the initial direction so that when the motorl reverses because of overtravel at high speed, the motor armature .must turn against the friction load of theoppositely rotating frictional flywheel. This provides an overload which causes the motor to start up much more slowlythan it would otherwise and the rate of speed increase is controllable by means of the friction load provided by adjusting the 'set screw 65.on the flywheel. Therefore, it is possible to cause the motor to stop within a much smaller angle and with a much narrower insulating gap in the electrical stopping device.

Furthermore, with the flywheel mounted on the motor shaft between fixed collars or other suitable means, it may not only rotate to provide a friction load on the shaft for controlling the tuning, but it may also provide axial inertia in a shifting armature type of motor'suflicient to vcause the clutching means to remain engaged during the deenergizing and reversal of current to the motor, as the stopping' device contact trav.

erses the insulating gap or segment during the over-travel movement of the tuning operation.

This prevents vunnecessary axial movement or chattering of the motor armature at each tuning point.

We claim as our invention: Y 1. In an electric motor control system for radiov apparatus and the like, the combination with a control device of a reversible electric motor hav ing a rotatable drive shaft connected withsaid device to operate it, said shaft being axially movable in response to the deenergizing of the 4motor, means carried by said shaft providing a clutch operable upon axial movement of said'` lshaft to disconnect the shaft fromsaid control device, a ywheel frictionally mounted on said shaft whereby said flywheel imparts axial inertia to said shaft tending to resist axial` movement and a frictional load4 on said shaft to reduce the initial speed of rotation upon reversal of said motor by reason of the continued rotation of said flywheel in the initial direction and fric- ,1li

tion between said flywheel and said shaft.

2. In a motor-driven radio tuning system, the combination of a drive shaft, tuning means having a movable element connected with the shaft and operative at -a lower speed than the drive shaft, electrical means'includng an adjustable device for deenergizing the motor at a preselected position in the tuning movement of said element and for energizing said motor to move said element toward said position from either side thereof, afiywheel device frictionally coupled to and driven by the motor whereby said device .is adapted to coast when said motor reverses the direction of rotation, to provide a braking load for and to reduce the speed of the motor in reverse, means providing a clutch in the connection between the motor and the movable tuning element, said clutch having an operating element connected with the flywheel device to move conjointly therewith axially in response to energizing and deenergizing of the motor, whereby the axial inertia of said device tends to resist momentarily the operating movement of said clutch element.

3L In a radio tuning control system, a tuning shaft, a reversible electric motor having a rotary drive shaft which moves axially in response to the energizing of the motor, means providing a restoring force for said shaft against which it moves, means connected with the tuning shaft for reversing the rotation of said motor following over-travel of and for stopping the motor at the same initial ,speed as in a forward direction when energized, by reason of 'rotating friction load imparted to said motor shaft by said device,

thereby to effect exact stopping of said tuning shaft at any one ofv said positions, and means providing a connection between said device and said shaft for imparting said axialinertia to said shaft.

4. In a motor tuning system for radio receivers, the combination with a tuning shaft, of a reversible tuning motor having `a shaft connected therewith, a clutch in said connection, a reversing device for the motor connected with said shaft and comprising two contact elements separatedby a relatively narrow insulating gap, at least one adjustable contact 'element positioned to engage sait/l` segmentsland lyingin thev path of movie'- ment of said insulating gap, said contact being slightly less in width than said gap, a reduction gearing between said motor and said tuning shaftrproviding a high rate of movement for said shaft such that the gap over-travels said Contact causing reversal of said motor, a iiywheel providing a frictional load against rotation of said motor upon reversal to reduce the speed of said motor, whereby said contact may be centered accurately on said insulating gap at the reduced speed, said ywheel being mounted on the motor shaft to rotate relatively thereto,

means providing an adjustable-friction connection between said iiywheel and said motor shaft whereby the initial speed of the' motor upon reversalmay be continued, means for operating said clutch by axial movement of the motor shaft,

and means providing a connection between the flywheel and the motor shaft tor applying the inertia load of the flywheel to the shaft in response to axial movement thereof.

HAROLD H. BEIZER. WILLIAMENEWHAN.

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