US2267135A - Motor tuning arrangement - Google Patents

Description

DecQZB, 1941. w, VAN ROBERTS 2,267,135

MOTOR TUNING ARRANGEMENT Filed June 10, 1959 INVENTOR W, WALTER VAN 5. ROBERTS ATTORN EY Patented Dec. 23, 1941 MO'lOlRl TUNING ARRANGEMENT Walter van B. Roberts, Princeton, N. 1., minor to Radio Corporation of America, a corporation of Delaware Application June 10, 1939, Serial No. 278,490

Claims.

The present invention relates broadly to motor circuits and more particularly to improvements in motor circuits employed as the driving means for adjustable elements of radio signalling apparatus.

In motor tuning devices of the type employing a disk and a cooperating sliding contact which devices are intended to be stopped by the sliding contact reaching an insulated portion or segment of the disk, the dliiiculty has arisen that if the insulating segment is made suiflciently narrow to insure breaking the motor circuit at a precise single point, then the inertia of the driving mechanism is liable to carry the sliding contact entirely across the insulated segment. When the disk is of the type which is so arranged that a reversible motor tends to turn the disk in such a direction as to bring the segment and the sliding contact together with the least travel, the result is that after passing the segment the motor reverses and comes back to it. It may even over-shoot the segment more than once and this behavior is what is termed hunting.

When the motor control circuit is of the type employing a single disk which is arranged so that the motor drives the disk in one direction only, so that the desired position is always approached from one side, the insulated segment must be made very narrow in order that closely adjacent stations may be tuned to in instances where the motor control circuit is utilized to operate a variable tuning instrumentality. In such cases the result of the sliding contact overrunning the insulating segment is that after passing the insulated segment, the motor is again energized thus causing a complete revolution of the disk. This may go on and on and thus prevent proper adjustment of the device. It is, of course, possible to eliminate this eifect in both the instances above discussed by running the motor extremely slowly but this involves an undesirable delay in the time-of tuning. v

In accordance with a feature of the present invention, rapid tuning is efiected by running the motor at high speed until the contact is near the insulating segment and then automatically reducing the speed of the motor so that upon reaching the segment there is not sufllcient momentum in the motor to carry the contact beyond the segment. In accordance with a further feature of the present invention, precise setting is insured mechanically by arranging the sliding contact so as to drop into a sharply defined notch in-the insulating segment, the size 01' this notch and the contact pressure being so related as to produce a torque on the disk sumcient to turn the tuning assembly in the absence of mechanical connection to the motor. It will be appreciated that when the contact is suddenly stopped by hitting the bottom of the notch, great force would be developed by the motor even though its momentum was very small it the mechanical connection between the motor and the disk were rigid. In accordance with another ieature of the present invention this difllculty is avoided by drivingthe disk through a mechanical coupling having a predetermined amount of lost motion.

The various novel features of the invention will be better understood by reference to the accompanying drawing wherein,

Fig. 1 illustrates schematically one form which the invention may take in a motor control circuit employing a plurality of adjustable contact elements cooperating with a single disk and wherein the disk is always rotated in one direction;

Fig. 2 illustrates in a schematic way the invention applied to a motor circuit which employs a so-called "split commutator and a reversible motor; and,

Fig. 3 is a schematic showing of a form of the invention in a motor control circuit wherein an individual settable commutator ring is provided for each station to be tuned to.

Referring to Fig. 1 of the drawing, l indicates a grounded metal disk rigidly attached to a shaft 2. The shaft 2 may be connected to any variable element that it is desired to operate such as a tuning condenser of a radio receiving system. A driving motor III which, as will be pointed out below, is coupled to the disk I through a means providing a small amount of lost motion, has one terminal connected to ground and the other to one side'oi a suitable source of voltage l2. Cooperating with the disk I are four adjustable sliding contacts 80, 9b, 9c and 9d. Each of the sliding contacts is connected to the other terminal of said source l2 through separate circuits which include respectively switches or push buttons Ila, llb, Ho and lid. It is to be understood that the motor rotates the disk I in one direction only as indicated by the arrow. The disk I is provided with two inserts or segments 5 and 5a. Segment 5 is made of insulation material and segment 5a is made of a conducting material which has an appreciably higher electrical resistance value than the mtaerial of which the disk I is made. Segment 5 is provided with a notch into which the ends of any one of the sliding contacts Sit-9d fits,

Let us now suppose that one of the switches l|a-l Id is closed to institute the operation of the motor I0. A circuit is completed from ground through motor III, source or voltage II, the particular switch or push button lIa-lld which has been closed, the sliding contact Sic-9d, corresponding to the push button which has been closed, 'disk I, back to ground, thus completing the circuit and operating the motor so as to turn the disk in the direction indicated continuation of the circle defined by disk I, is

chosen suflicient for the motor to slow down to a speed such that upon breaking its circuit itwill not coast as far as corresponds to the amount of lost motion provided by the coupling between the motor and the disk. When the sliding contact reaches the portion of segment 5 where the profile is cut away to form a notch,

the pressure on the sliding contact causes the disk to jump ahead and take up the, lost motion.

The angular distance between the bottom of. thenotch and the junction of segments 5 and 5a is preferably chosen less than the angular lost motion so that even were the motor to stop just as the sliding contact passes the junction between segments 5 and 5a the lost motionwould have already permitted the sliding contact device to reach the bottom of the notch. On the other hand the motor may coast a" distance corresponding to the lost motion beyond its position at the time the slider reaches the bottom of the notch without taking up the lostmotion and affecting the proper seating of the sliding contact in the notch.

In the arrangement shown in Fig. 1 the operator has closed the switch or push button Ho and the motor III has rotated the disk I in the direction of the arrow to the point where the sliding contact 90 is in contact with the high resistance segment So so that in effect resistance has been inserted in the motor circuit thus slowing down the motor. Thus the disk is driven at a reduced speed until the sliding contact 9c hits the insulating segment 5 at which time the motor circuit will be broken even though the switch or push button I I is maintained closed. The pressureof the sliding contact Be on the disk I will force the disk to rotate by taking up the lost motion until the sliding contact 90 is flrmly'seated' within the notch formed within the insulating segment}. The switches Ila-lld are of the type that spring open when the operator releases'then'i. It is to,be understood, of course,

' that the motor operates the disk I at a high speed upon closure of anyof switches Ila-I Id 'when-the -corresponding sliding contact 90-911 located anywhere except in contact with :either segment or segment So so that if we that switch Ila is closed the motor I0 will operate the disk I at high speed until the segment 5a reaches the sliding contact So at which time the added resistance which the mo-. torcurrenl; encounters through segment 5a slows down flie motor.

I It is not necessary that segment 51: be composed a: high resistivity material as it may be a i segment insulated from the body oi the disk except by way of a lumped resistance path. Such an arrangement has been shown in Fig. 2 of the drawingwherein the disk I is this time composed or suitable insulation material and the commutator is made up or two sections In and lb fixed to the outer portion of the disk I. The shaft 2 in this case is driven by reversible motor Ilia through a coupling having a predetermined amount of lost motion. The segments la and 6b separated by the insulating segment 5 are connected respectively to sections In. and lb oi the split commutator through lumped resistors 8a and 817 respectively. ments 6a and to may be made out of exactly the same material as the material of which sections Ia and lb'of the commutator are made.

, The remaining portion of the circult'shown in Fig. 2- is thesame as that shown in Fig. 1 except that due to the fact that a reversible motor is employed two sources ofthe voltage Ila and I2!) are provided. The arrangement shown in Fig. 2

. operates as follows:

Suppose that switch or push button lie is depressed or closed as shown thenthe motor circuit is completed as follows: From ground through switch I Ic,sliding contact 9c,segment8a,

I resistor 8a, section Ia of the commutator, battery I'ia, motor Ilia, back to ground. The motor Illa which is provided with a suitable field 10b here 3, -shown' generally as a magnet with south and 1 north poles, being'energized-by the battery Ila will rotate the shaft 2 counter-clockwise at a reduced-s'peed (due to resistor 8a being in the motor circuit) until the sliding brush or contact 9c reaches the insulating segment '5 at which time the motor circuit is broken and the spring force of the sliding. contact 90 rotates the disk 1 until the contact is seated in the notch as previously described in connection with Fig, 1. If the switch Ila had been operated, the motor circuit would be completed through sliding contact 9a,

, section .Ib of the commutator and battery Ill),

insertion of resistor 8b in the motor circuit.

thus causing the motor Illa torotate the disk] clockwise ata high speed until segment 06 reachedsliding contact So at which time the speed of the motor would be reduced due to the Then upon the insulating segment 5 reaching the brush 9a the motor circuit would be broken and the spring force of sliding contact would" tak up the lostinotion between the motorand the disk and accurately seat itself in the notch. It is to be understood that the amount'or insulation at the junction of segment to and "segment Ia, and at the junction of segment") and section Ib is suificiently narrow so that the mo! mentum of the device prevents the system from stopping when the particular brush all-9b corresponding to the push button I-la-lld depressed; reaches the insulated junction area.

Reference will now be had to Fig. 3 which shows in detail the arrangement for providingcoupling with lost motion between the motor and the disks. For this purpose the end of the shaft 2' which is near the motor is provided with a square cross section which fits into square hole I! formed in the gear I4. The gear I4 is in meshwith pinion I5 attached to the shaft of motor ll. The

shaft 3 is sufiiciently smaller than the hole I! in gear I4 to provide a predetermined small amount a suitable resilientmaterial in order 'to reduce In this way the segmechanical shock when the lost motion is taken up. It is to be understood, of course, that lost motion may be introduced in a variety of other ways with equally good results. The mechanism shown in Fig. 3 utilizes a separate commutator for each station to be tuned to by the condenser II the rotor of which is attached to the shaft 2. Thus, commutator It may be adjusted on the shaft 2 by a suitable set screw or other arrangement not shown so that the position of the insulation segment 5 corresponds to the position of the condenser at which a desired station is tuned to. It is to be understood that the segments Ii and 5a of commutators I and i1 correspond to the two segments bearing the same numerals of the commutator I shown in Fig. 1. For tuning to another station by means of push buttons or switch Ila another disk i1 is provided which is also adjustable on the shaft 2 to any desired position. The brushes lid and lib are spring pressed on the commutators in any suitable fashion.

One particular construction that is found to be suitable is to construct the brushes lid and lib of resilient material and mount them on suitable blocks I91: and I9!) respectively in such a way that the correct amount of pressure is exerted upon the periphery of the respective disks or commutators I1 and I6 so that the force exerted by the brushes is sufilcient to seat the V- shaped ends of the brushes accurately within the notches provided in the insulation segments 5 as previously described.

In Fig. 3 the metal disks l6 and I! are grounded through the shaft 2 and a suitable ring and brush arrangement 20. While only two disks have been shown it is to be understood that any number thereof may be utilized depending upon the number of stations desired to be tuned to automatically.

The description of the illustrative embodiments is not intended as defining the limits of the invention, and it will be understood that the invention may be variously modified and embodied within the scope of the appended claims.

I claim:

1. In a motor control system an adjustable shaft, a contact member of conducting material mounted on said shaft, said contact member being provided with a section of insulation material formed along a portion of its surface, a notch formed in said-section, a motor for driving said adjustable shaft, a motor circuit completed through said contact member, said motor being coupled to said shaft through means having appreciable lost motion whereby said shaft may be adjusted within the limits of said lost motion without rotating said motor, an auxiliary driving means for said shaft comprising a spring pressed device positioned so as to slide along the surface of the contact member and arranged so as to be forced, through the action of the pressure exerted by the spring, into the center of the notch formed in the insulation section when the shaft is adjusted to a position element, said contact element being arranged to slide over a predetermined portion of the surface area of the conducting ring assembly, a pair of adjacent inserts formed in said ring inthe path of said contact element, one of said inserts being composed of insulation material for breaking themotor control circuit when the contact element is over said insulation insert, the other of said inserts being composed of a conducting material which has a higher electrical resistance than I the material of which the conducting ring is made for inserting a resistance in the motor control circuit sufllcient to operate the motor at a reduced speed when the contact element is over said last named insert.

3. The invention defined by the next preceding claim characterized by that the insert of insulation material is provided with a notch into which the brush contact element is forced by means of a spring when the ring assembly is adjusted to a position where the brush contact element is just entering the notch.

4. In a control system for signalling apparatus having an adjustable member, a motor mechanically connected to said member for driving the member to be adjusted rapidly toward a predetermined position, means for slowing down the motor prior to reaching said position, means for entirely discontinuing the driving torque of said motor subsequently to said slowing down but prior to reaching said position, lost motion in the mechanical connection between said motor and said member and mechanical means for bringing said member accurately to said predetermined position from theposition occupied at the cessation of said torque.

5. In a motor control device, a member to be adjusted;a motor coupled to said member through a device having a predetermined amount of lost motion, a motor circuit including means for controlling the operation of the motor so as to adjust said member rapidly toward a predetermined position and means for slowing down the motor prior to said member reaching said position, means for de-energizing the motor subsequently to said slowing down but prior to reaching said position and mechanical means acting independently of the motor for bringing said member accurately to said position through take-up of said lost motion.

6. In a motor control circuit for a motor which is adapted to adjust an adjustable member to any one of several different predetermined positions through selective operation of anyone of a plurality of selectively operable means, means for coupling the adjustable member to the motor through a device having a predetermined amount of lost motion, means controlling the operation of the motor so as to adjust said member rapidly toward a selected one of said predetermined positions when the amount of adjustment of said adjustable member necessary to reach the selected one of said positions is greater than a predetermined amount, means for operating the motor at a reduced speed when the remaining amount of adjustment necessary to reach the selected position is in a range bounded by said predetermined amount and a position just short of the desired selected position, means for de-energizing the motor when said position which is just short of the selected position is reached and means acting independently of the motor for bringing said member accurately to said desired position through take-up of the lost motion.

7. In an arrangement for adjusting a variable device to any one of a plu ality of desired positions, a movable member movable with said variable device, an electric motor coupled to said movable member through means provided with a predetermined amount of lost motion, said movable member being provided with a contact surface composed of conducting material, a brush contact device positioned with respect to said movable member so as to be in sliding contact with said contact surface, said contact surface having provided thereon a segment of insulation material having a V-shaped notch formed therein, said brush contact device being proportioned in respect to said notch so that the contact device can slip into and be held substantially snugly within the notch when the movable member is in such a position that the notch portion of the contact surface is under the brush contact device, said contact surface and cooperating brush constituting a switching means which is effectively closed in all positions of the movable member when the contact brush device is in sliding contact with the portion of the contact surface composed of conducting material and effectively open in all positions of the movable member where the brush device is entirely in sliding contact with the segment of insulation material, a pair of terminals adapted to be connected to a source of motor operating voltage, circuit means including said switching device for connecting the motor across said terminals, means for mechanically pressing said contact device against said contact surface with-suflicient force to accurately center the contact device within said notch by movement of said movable member through take-up of said lost motion and independently of the driving motor, when the movable member is adjusted to a position at which the contact device is just entering the notch.

8. In an arrangement of the type described in claim 7 wherein a section of said contact surface composed of conducting material and adjacent the segment of insulation material is composed of a material which while conducting has substantially greater electrical resistance than said first named conducting material whereby a resistance is in effect inserted in said circuit means in all positions of the movable member where the contact brush device is in sliding contact with said high resistance portion of the contact surface.

9. In an arrangement 'of the type described in claim 7 wherein a section of said contact surface composed of conducting material adjacent the segment of insulation materialis insulated from the contact surface composed of conducting material except for a connection thereto through a resistor element whereby a resistance is effectively inserted in said circuit means in all positions of the movable member where the contact brush device is in sliding contact with said section of the contact surface adjacent the segment of insulation material.

10. In a motor control system, an adjustable member, a motor for actuating said adjustable member to diflerent predetermined positions, a source of voltage for said motor, position determiningmeans associated with said motor and including a conducting ring member coupled to said adjustable member and movable therewith and a brush contact device slidable along a portion of the surface of the conducting ring, an electrical circuit including said source, the motor and a sliding connection between the conducting ring and the motor, a section of insulation material formed on a. portion of the surface of the conducting ring over which the brush slides for interrupting the motor circuit when said brush contact device is over said insulation material portion of the'conducting ring, another portion of the conducting ring along the surface over which the brush contact slides and located adjacent the iusulation section being formed of a conducting material which has sufflciently higher electrical resistance than the main part of the conducting ring to cause appreciable reduction in speed of the motor when the brush contact device is over said last named portion of the conductingring.v

WALTER van B. ROBERTS.

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