US2391470A

US2391470A - Automatic tuning apparatus

Info

Publication number: US2391470A
Application number: US487305A
Authority: US
Inventors: Richard W May
Original assignee: Collins Radio Co
Current assignee: Collins Radio Co
Priority date: 1943-05-17
Filing date: 1943-05-17
Publication date: 1945-12-25
Anticipated expiration: 1962-12-25

Description

ec. 25, 1945. R. W, MAY 2391,47@

AUTOMATI C TUNING APPARATUS Filed May 1'7, 1945 4 Sheets-Sheet l zz J4 @a ji' j l A x9 rf r//l/f/l/g/ 6,/

Rw. MAY 2,3%479 y Dec. 25, 1945.

4 She Dec. 25, 1945. R, W MAY 2,391,470

AUTOMATIC TUNING APPARATUS Filed May 17, 1943 4 Sheets-Sheet 3 awa 'f/ zdf/fz Dec. 25, 1945. R W MAY AUTOMATIC TUNING APPARATUS Filed May 17, 1945 4 Sheets-Sheet 4 @ZW/ 6 Si Patented Dee. 25, 194s NTED ST Richard W. May, Cedar E Collins Radio Company,

Application May lll, 1949, Serial No. 487,395

(tCl. Ri-T142) ll Claims.

This invention relates to automatic tuning ap paratus for positioning a shaft at a desired point in any of a plurality of revolutions, and more particularly to a limit switch particularly designed for such tuning apparatus.

One feature of this invention is that it enables, without mechanical diiliculties, proper electrical limit control of automatic tuning means for use with a radio tuning shaft rotatable through a plurality of. revolutions; another feature of this invention is that rotation of the limit switch shaft may continue, after operation of the switch means, for as long as may be desirable without jamming of the operating parts;l still another feature of this invention is that the actuating mem-u ber for actuating the switch means is driven by a shaft rotatable through a large number of revolutions, preferably similar to the rotation of the tpned shaft; and yet another feature of this invention is that the actuating member 'is rotatably mounted on a nut on the limit switch threaded shaft with readily adjustable frictional engagement. Other features and advantages of this invention will be apparent from the following speciication and the drawings, in which:

Figure l is a schematic diagram of apparatus embodying my invention, with the parts in one terminal position; Figure 2 is a schematic diagram of one portion of that shown in Figure 1, but in. a different position; Figure 3 is a schematic diagram similar to Figure 2, but with the parts in still another position; Figure 4 is a schematic diagram similar to Figure 3, but with the parts in still a different position; Figure 5 is a side elevation of a shaft positioning unit adapted to automatically position a shaft at any desired point throughout a range of a plurality of revolutions, hereafter termed a multi-turn" unit; Figure 6 is a transverse sectional view of the slip clutch, along the line 6 6 of Figure 5; Figure 7 is a. sectional vlew of the multi-turn unit, along the line l-l of Figure 5, with a portion of the limit switch actuating member broken away; Figure 8 is an elevational view, partly in section, of the ratchet and one end of the selector cam assembly; Figure 9 is a fragmentary enlarged side elevational view of the limit switch, with the moving parts being shown in solid lines at one limit of their movement and in dotted lines at the other limit; Figure 10 is a view along the line lll-l0 of Figure 9,v partially broken away; and Figure 11 is a wiring diagram of a circuit adapted to operate the particular embodiment of my invention shown.

The multi-turn shaft positioning unit disclosed in this application is an improvement on auto- I liti apids, iowa, assigner to a corporation oi Howe.

matic tuning apparatus mechanically positioning the' shaft of a tuned element automatically as the result of a sequence of operations initiated by movement of a control switch. Apparatus oi this general type has been the subject of a number of patents issued to one Arthur A. Collins, one of the more recent of these patents being No. 2,285,414, issued June 9, 1942.

The automatic tuning arrangements which are the subject of such previous patents were all designed for and operable only in connection with a shaft designed to be rotated through an arc not exceeding one revolution, suilcient for the tuning of elements such as a conventional condenser, 'tap switch, or the like. Certain elements of a radio set, however, can be better tuned by a shaft rotat able through a plurality of revolutions.. example, a permeability tuning core is preferably moved in or out of its cooperating coil by rotation of a threaded lead screw which may rotate through twenty turns to vary the inductance from minimum to maximum; and certain types of condensers and carbon pile resistors are preferably driven by lead screws.

The said Arthur A. Collins has recently developed a multi-turn shaft positioning unit and associated operative mechanism and control circuit capable of rotating the shaft of a tuned element through any number of desired revolutions and of stopping the shaft automatically with a high degree of accuracy at any desired point in the entire range of movement. The general principles and major combination of elements of a multi-turn unit, and some of the detailed improvements thereof, have been invented by the said Arthur A. Collins and are the subject matter of his co-pending applications, Serial No. 472,717, led January 18, 1943, and Serial No. 483,899, led April 21, 1943. Certain other speciiic portions of a multiturn unit have been improved by me. An improved limit switch specilcally designed for such an automatic tuning device is the subject of this application; and certain other features are covered by my other co-pending applications, Serial For l No. 515,250, led December 22, 1943, and Serial l of switch to select similar stop combinations in\ all of the units, whereupon the various circuit elements would be instantly and automatically tuned to thedesired .predetermined frequency. For simplicity of explanation only a multi-turn unit is shown here, but it will be understood that this can be used in combination with single turn units of the kind previously shown in issued patents or of the kind shown in the aforesaid Collins application, Serial No. 472,717.

In the particular embodiment of the invention illustrated here, .and referring now more particularly to Figure 1, the schematic diagram, a reversible electric motor 20 drives a main shaft 2i which in turndrives a cross shaft or line shaft tional line shafts may be provided.

The main shaft of the multi-turn unit is the rotatable shaft 24 which operates through a lead screw arrangement to move a permeability core or tuning slug 25 axially of a coil 26, this core being so mounted (as by a splinedarrangement not shown) as to enable axial movement while preventing rotational movement thereof. Mounted on a drum on the shaft 24 in a manner to be hereafter more fully described (normally non-rotatable with respect to the shaft) are a plurality of tuning stop rings 21, a' manual stop ring 28 (which may be part of the vstop means on the stop ring mounting drum), and a terminal stop ring 29. While all of these are non-rotatably locked to the shaft 24 during operation, the tuning stop rings 2l may be unlocked to permit setting or vpre-selection of the point at which the shaft is to stop. A worm on the line shaft 22 drives a worm gear 3l (as at a 121/2 to 1 ratio, for example), the worm gear driving one of the two elements of a slip-clutch 32,l the other element of this clutch being connected to and driving the shaft 24.

The worm gear 3i also drives a limit switch, lhere indicated in general as 33, through a slipclutch arrangement indicated as 80. A threaded shaft 8l carries an operating arm 82, this being shown in the terminal position of a cycle of operation, with the movable contact 83 out of en gagement with the contact 84. Upon initiation of a cycle of operation by manipulation of the selector switch to call for a new frequency setting, the operating arm 82 travels to the left (83 iirst engaging 84 and moving it out of engagement with 85) until contact between 86 and 8l is broken, the motor thereafter reversing as will be more fully described later in connection with the circuit diagram (Figure 11), whereupon the limit switch arm reverses and travelsback to its terminal position shown in Figure 1 of the drawings.

Another worm 34 on the line shaft 22 drives a worm gear 35 (as at a 40 to 1 ratio), this in turn acting through a single-tooth ratchet, here indicated in general as 36, to drive (in one direction only) a shaft 31. This shaft has non-rotatably mounted thereon a plurality of tuning selector cams 38, a manual selector cam 33, and a terminal stop ring (which may be part 'of the cam drum). Another shaft 4I carries a plurality of ,22. This one line shaftmay drive a number of separate'tuning units simultaneously,lor addithe shaft 4|. but the secondary cams are mounted with a frictional retention su-ch that they normally move with the shaft, but can slip if the frictional force is exceeded. The shaft 4i is driven from the shaft 24 in fixed relation thereto.

by gearing, here indicated in general as 45, appropriateto the number of turnsl for which the unit is designed, as for example with a gear ratio of 23% to 1.

A stud 48 provides a mounting for a plurality of automatic tuning pawls 4l, a manual tuning pawl 48, and a terminal stop pawl 49. The pawls 4l and 48 are biased in one direction by the rod springs 60 and 5I, while the terminal stop pawl 491s normally biased to a position intermediate the full line and dotted line positions by a coil spring 52.

Referring first to the terminal position pawl,

all of the parts are shown at one terminal, where 'ure 1), while the ring 44 would begina corresponding clockwise rotation at a greatly reduced rate. As soon as this latter ring moved a, few degrees the terminal stop pawl 49 would be permitted to assume an intermediate position under the influence of the spring 52, and the shaft 24 would be free to rotate through a desired number of revolutions (as a little over twenty revolutions) until the shoulder 44a had come around to its dotted line position and forced the terminal stop pawl 49 to its dotted line position, whereupon the shoulder 29a would engage one of the ends of this stop pawl and stop the tuned shaft at its other terminal position, hereafter designated the "home position. Then as soon as the sequence of loperations. effected reversal of the motor 20 the shaft 24 and its associated rings would begin to rotate in the reverse or clockwise direction, being free to rotate in this direction until stopped -by one of the tuning stop combinations or by the terminal stop arrangement as illustrated in solid v lines.

When automatic tuning is eiected by the sequence of operations to be hereafter more fully described, one step is the selection of the tuning pawl 4l which is to be rendered operative. This is accomplished by rotating the selector cam drum until the slot 38a lies immediately under the portion 41a of the pawl, the pawl then moving slightly (under the inuence of the spring 50) until the end 41h drops down onto the periphery of the secondary cam 42, this position 'of the parts then'continues rotation (in a clockwise direction,

secondary or turn determining cams 42, a. sec- 44. This latter cam is immovably mounted on speaking with respect to these views) until the end 41e of .the pawl drops into the slot 21a and strikes whatmay be termed the forward shoul- 'der 21h of this slot, this situation being illustrated-'in Figure 4. This stops rotation of the shaft 24 although, because of slippage in thev clutch 32, the line shafts and other units may continue until the cycle of operation is terminated.

It will thus be seen that a desired number ofautomatic stop combinations may be provided, each being a duplicate of the combination just described. Each. such combination includes means for selecting that combination, one of the selector cams; means for determining in which turn or revolution of the shaft 24 the pawl will be permitted to move into operative relationship with the stop ring 21, this means comprising the secondary cam 42; and means for stopping the shaft of the tuned element at a desired point in the chosen revolution, this being effected by engagement of the end of the pawl with the forward shoulder of the slot of the stop ring 21. The shafts 24 and 4I, and thus the stop rings and secondary cams, are maintained in synchronizatlon and moved in appropriate ratios to each other by the interconnecting gear train 4l, so that whenever a given stop combination is selected the shaft of the tuned element will be stopped very accurately and precisely at the chosen point in the chosen revolution, which point may be anywhere through a full range of continuous rotation of the shaft 24.

While the full sequence cf operations of an automatic tuning cycle will be explained in detail later in connection with the description of the various switches and relays effecting such sequence, itis believed that understanding of the present invention will be facilitated by a brief description of a tuning operation at this time. When it is desired to change the transmitter to a different predetermined frequency the operator turns a control switch to the corresponding setting, whereupon the motor 20 starts to rotate in a direction moving all of the parts toward home position. The motor rotates through a predetermined number of turns determined by the limit switch, various tuned shafts reaching home position at various times (depending on their previous positions) and their respective clutches thereafter slipping. When this portion of the cycle is completed the motor continues operation in the same direction ("beyond home, as it might be termed) being stopped somewhere during this additional rotation by an automatic selector switch, stoppage of the motor occurring when the selector cam arrangements are in such position as to actuate the desired stop combination, the one corresponding to the control switch setting. Thereupon the motor reversesand drives the parts in the tuning direction (but without disturbing the selector cams), the various units rotating in this direction until each tuned shaft is stopped by the selected pawl at a position appropriate to the frequency desired, the respective clutches thereafter slipping until the motor and lines shafts have completed the full cycle and have been stopped by the limit switch.

In order to effect selection of the desired stop combination the shaft 31 rotates, through a lost motion connection comprising the parts 60 and 6I, the rotatable portion 82a of an automatic selector switch or circuit seeking switch 62. This switch comprises a plurality of fixed taps or contacts 63a-l and a rotatable member adapted to make contact with all of the taps except one which lies within the confines of a slot in this rotatable member. While the unit illustrated here is shown as having both a limit switch and a selector switch, in order that an operable unit may be shown, it will be understood that only one of the units in a radio set need have these elements. All of the selector cam assemblies in the various units, however. must rotate in proper synchronization and registration with the selector switch 62, and this is accomplished by appropriate gearing and by the use of the singletooth ratchets. It will be noted that there is no slip-clutch in the drive for the selector cam arrangement; and accordingly, the driving elements of the single-tooth ratchets 36 in all of the various tuning units rotate in fixed relation to each other. Since the ratchets are of the single-tooth variety this synchronization of the driving elements automatically results in synchronization of the driven elements, so that all of the various selector cam arrangements upon the initiation of each tuning cycle assume a synchronized relation with each other and then rotate together until they are stopped to make corresponding selections of stop combinations in all of the various tuning units. The lost motion connection comprising the parts 60 and 6I is used to enable the selector cams 38 to back off or shift position slightly as the portion 41a of the pawl drops into the selector cam slot. This movement of the selector cams must be permitted without movement of the selector switch 62, since any movement of the rotatable portion of this switch which would cause the edges of its slot to again con-tact the switch point 63a would cause undesired disturbance of the cycle ofoperations.

The provision of a manual selector cam 39 and cooperating pawl 48 .prevent any accidental and undesired operation of one of the tuning stop combinations when it is desired to manually tune the shaft. When manual tuning is selected, movement of the portion 48a into the slot 39a locks the selector arrangement against rotation, so that vibration will not accidentally bring a tuning stop combination into operation. When the manual arrangement is actuated there is no hindrance to manual rotation of the shaft 24 as there is no projection on the outer end 48e of the manual pawl, and it cooperates with a smooth ring 28.

Referring now more particularly to the structural arrangement as illustrated in Figures 5 8, it will be seen that the parts are mounted in a self-contained unit between the plates 65 and 66 held in proper relation to each other by posts 61. A tuned shaft 24 carries an appropriate number (as I I) tuning stop rings 21A- K and the terminal stop ring 29, these being separated by spacer rings 69 keyed to a drum on the tuning shaft. Means is provided for selectively locking or unlocking the tuning stop rings 21 on the shaft 24 (not shown in detail here), this means being operated by the manually rotatable operating bar Ha in the dial 10. Unlocking is only for the purpose of setting the tuning stop rings to a desired position, and operatively they act as though they were at all times rigidly mounted on the shaft 24.

The secondary cams 42a-k are mounted on an appropriate drum on the shaft 4 I, with operating rings between them. the arrangement being simisecondary cam shaftii. isgeared-to the main shaft 24 any change in the setting of this latter eects a similarsetting of whichever secondary cam is in engagement with a stop pawl at that time.

Referring lnow more particularly to Figure 6,. it will be seen that the slip clutch 32 comprises as its two friction parts an annular shoe 02a 'oi' non-metallic material (as fiber or plastic) encircling a metal drum 32h ilxedly mounted on the shaft 24. The annular shoe is held in place with the desired amount of frictional engagement by the encircling band spring 32e. The worin gear 8|, rotatable about but not connected to the shaft 24, carries a stud 32d lying between the two end faces of the shoe 32a, the operation preferably providing a little clearance or lost motion. Rotation of the worm gear 3| by the worm 30 therefore transmits its force to the shaft 24 by pressure against one or the other of the end faces of the friction shoe 32a; and when the frictional grip of the shoe 32h is exceeded, the worm gear 3| can rotate without rotation of the shaft 34, slippage taking place between the shoe and the drum. i

The details of the single-tooth ratchet are best seen in Figure 8. The driving element 30a is fixed to the worm gear 35, both being freely rotated about the shaft 31; while the driven member 36h is xed to this shaf-t so that movement of the driven member eects movement of the selector cam shaft 31. The driving member 38a is providedv with an annular slot 36e having a fixed (pin 36d in one portion thereof, this pin having a sloping face. The cooperating driven member is provided with a bore or opening 38e in which a pin 36] is longitudinally movable against the force of a spring 36g, the bore registering with the annular slot. Rotation of the driving member in one direction (its direction of rotation during the tuning portion of the cycle) brings the sloping face into engagement with the movable pin and does not effect rotation of the driven shaft; rotation in the other direction (when the parts are being driven toward home position), however, causes driving engagement between the pins and rotation of the selector drum and cams.

Before describing the limit switch in detail the general operation of the device will be described, with particular reference to the circuit diagram, Figure ll. A battery is illustrated as representative of any appropriate source of power for the motor and relays. The motor control relay |02 has an actuating coil |02a, three movable switch members IDZb-d, three "upper contacts |02e-g, and three lower contacts |02h-j. This motor control relay and the limit switch 33 cooperate to achieve the desired sequence of operations.

A manual selector switch, here identified in general as |03, is shown as having I2 switch taps i a-l wired `to the corresponding switch points 63 a-Z of the automatic selector switch, the manual switch arm |03m being' adapted to engage any one of the i2 switch points and thus to complete a circuit to any one of the correspending automatic selector switch taps. The switch |04 is shown in a position enabling control by this manual selector switch; but when the switch |06 is thrown to its other contact a control switch of any desired type at some remote point may be operated. A relay has cooperating contacts |05c and |05e which control the tuning circuit, and other contacts which may assumo control carrier emission or any other desired circuit, this and the manual switch |08 providing an interlocked action so that traon is not effected while the automatic tuning/device is operated.

Assuming that the parts are as shown in Figures 5-8, and it is desired to select another frequency setting, movement of the switch arm 103m might be made to the contact |03lc, vas shown in dotted line position. This movement completes a circuit from ground through disk 82a, contact 63k, wire |01, contact |03k, arm |03ml wire |08, switch |04, relay |08 (it being assumed` that the carrier control switch |06 is open and the coil |05a not energized), wire |00, motor relay coil I02a, wire H0, battery |0| and wire |I| to ground. This energizes the motor control relay and causes its movable switch elements |02b-d to move from the positions shown to their lower positions. This energizes the motor 20 by a circuit including wire H0, contacts |02c and |021, the motor armature,

i, contacts |0212 and |0211., and wire back to the battery. This effects rotation of the motor in the home direction. the ratchet backing up the selector cam drum and lifting the pawis 41h out of the secondary cam and stop ring slots. At the same time the actuating member 82 of the limit switch 33 begins to travel downward and contact 33 makes engagement with the contact 84, breaking its contact with 85 and disabling the carrier control switch |06 until the tuning cycle is completed. The disk 62a of the automatic selector switch is also rotating during this operation but intermittent breaking of the contacts 63k has no eiect because a holding circuit for the motor control relay has been energized through the limit switch contacts 86 and 8l and relay contacts |0211 and |02j.

I'he motor continues operation until the tuned shaft has reached home position, the clutch thereafter slipping until the actuating member 82 of the limit switch opens the holding circuit contacts 8S and 81. This returns control to the automatic selector switch t2, and as soon as it reaches a position with its slot opposite the contact 03k the motor control relay circuit is deenergized and the motor reverses, leaving the selector cams in a position corresponding to the selector tap 63k, rendering a desired stop combination operable. l

Return of the movable parts of the motor control relay to the position shown in the drawings completes another circuitto the motor in such a way as to cause its operation in a reverse direction, as mentioned, this circuit including wire i0, contacts |020 and |02f, wire H2, contacts 03 and 00, wire H3, contacts |021) and |026, the motor armature, contacts |02d and |029, and Wire back to the battery, it being noted that the upper end of the battery is now connected to the lower end of the armature, the reverse of the previous case. This causes movement of the various tuning device partsfin the tuning direction, this continuing until the tuning shaft is stopped in its appropriate position by engagement of the chosen pawl with the forward shoulder of its cooperating stop ring slot (as illustrated in Figures 4 and 7), the clutch thereafter slipping to permit the motor drive to continue to terminal position. This terminal position is determined by opening of the

limit switch contacts

83 and 84 by the actuating member 82. A bridging resistor Ht is associated with these contacts to always provide just enough current to keep the pawl in firm enf sagement with the shoulder of its cooperating stop split, the two split 92 threaded into a stud 94a.'

`ing with respect to to overcome the limit switch should have corresponding rotation.

In order to enable this to be accomplished within reasonable limitation of space and with a. good degree of accuracy the rotatable portion of the limit switch is made inthe form of a threaded shaft member 8i. As may be best seen in Figures and 7, the shaft 8l is geared to the driving element of the clutch 32 by gears 8B and 89 of equal size (the gears 3| and 8.9 being rigidly fastened together), so that rotation oi' the shaft si always corresponds exactly to that of the line shaft.

is may be best seen inFigures 9 and'lO, enlarged views, the shaft di has threaded thereon a nut all with a cylindrical bearing portion Qta on which the actuating member 82 is/rotatably mounted for frictiona'l engagement therewith, the parts being heldin desired relation by the iianges 99h and 90o on the nut. As may be best seen in Figure 7, the actuating member 82 is centrally portions 82a and 82h being urged together by the force of a spring iii, this being readily adjustable by rotation of the stud cooperating sleeve 92a in the portion 82h oi the actuating member. The outer ende of the actuating member are provided with a semi-circular groove or depression embracing the post @la to permit axial but prevent rotationai movement 'ofthe actuating member.

Thev cycle of operations of the tuning device, particularly at the home end where the selector cams must be positioned, requires that the tuning shaft (and thus the threaded shaft iii of the limit switch) rotate after the actuating member has reached its home terminal position (shown in dotted lines in Figure 9) and opened the contacts tt and til; and there is a certain amount of overrun at the other terminal position (shown in solid lines). In order to stop the actuating member, Without jamming or sticking of the threaded shaft 8|, I have provided the slip clutcharrangement between the nut 99 and the actuating member 32 as previously described, and means for positively rotating the nut within the actuating member.

In order to eiiect this rotation, collars 93 and 94 are rigidly mounted on the threaded shaft at site direction, the

' tively rotated each end thereof, the collar 93 having a projecting shoulder portion or stud 93a and the collar 94 having a similar projection shoulder portion or The nut is provided with cooperating shoulder portions on each side comprising the f'

studs

90d and 90e. If the parts be assumed to be in the positions shown in solid lines in Figure 9, at the beginning of a tuning cycle, initiation of the tuning operation by movement of the manual switch arm ||l3m starts the threaded shaft 9| rotating in a counter-clockwise direction (speak- Figure 10) in exact correspondence with the rotation of the driving elementof the clutch 32. Since the studs 94a and 90e are in the relation shown in Figure 10, the stud 94a can move away (counter-clockwise) with no frictional resistance of any kind to suchmovement: and the actuating member 82 starts to move along the shaft to the left (as shown in Figure 9), the friction al engagement between it and the nut preventing rotation between these two parts. As the actuating member moves to the left, its motion '1, wherein the last e'ects a change in the relationship of the

contacts

83, 34 and 8B, as previously described; then moves through the desired period of drive motion (slightly more than twenty turns in the unit illustrated); and finally strikes contact 86 and'opens its engagement with contact 8l. Just after this has been done the moving parts reach the position shown in dotted lines in Figure 9 and stud 93a comes into contact with stud 90d, in a squared and non-wedging engagement of the same kind illustrated in Figure 10. This engagement causes rotation of the nut within the actuating member, this latter member slipping on the bearing surface Qta. Yet despite the force required to cause this slip-clutch action, the studs 93a and 90d are in such relation that whenthe motor reverses and the threaded shaft 8i starts to rotate in the oppoactuating member and nut may start to move back to their initial position with no i'rictional resistance or hindrance to the starting of such movement. That is, while the nut is posieach end of the travel of the latter, this positive rotating means does not wedge or jam in any way and the parts release instantly and move back in the other direction upon within forces Well within that provided by the slip-clutch frictional engagement.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable oi many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the lspirit and scope of the invention as disclosed in the appended I claim:

i. In Aautomatic tuning apparatus for positioning a rotatable shaft, including reversible drive means adapted to rotate the shaft through a piurality of revolutions, a slip clutch in the connecclaims.

tion between the drive means and the shaft, a

plurality of stopping to stop the shaft at where in its range means, each being adapted a predetermined point anyof rotation, and selecting means for rendering operative a desired one of said stop means, this selecting means including a rotatable selector switch, a limit switch including: a threaded shaft member; switch means adjacent at least one end of the threaded member; a nut on said shaft; an actuating member 'rotatably mounted on said nut and having appreciable frictional engagement therewith, one of said members being adapted tobe rotated by and in accordance with rotation of the drive means, movement of the actuating member along the threaded shaft being adapted to operate the switch means; and means for causing the nut to rotate with the threaded shaft at the desired limits of movement of the actuating member.

2. Apparatus of the character claimed in claim 1, wherein the last mentioned means includes shoulder means on the nut and cooperating shoulder means rigidly mounted on the threaded shaft.

3. Apparatus of the character claimed in claim mentioned means includes shoulder means on each side of the nut and cooperating shoulder means rigidly mounted on the threaded shaft at each end thereof.

4. In automatic tuning apparatus for positioning a rotatable shaft, including reversible drive means adapted to rotate the shaft through a plurality oi revolutions, a slip clutch in the connection between the drive means and the shaft, a plurality of stopping means, each being adapted within the actuating member at reversal of the motor a rotatable selector switch, a limit switch in' cluding: a threaded shaft member adapted to be rotated by and in accordance with rotation of the drive means; switch means adjacent each end of the threaded shaft; a nut on said shaft;

an actuating member rotatably mounted on saicly nut and having appreciable frictional engagement therewith; means preventing rotational but permitting axial movement; of the actuating esonero threaded shaft member; a nut on said shaft; an actuating member rotatably mounted on said nut and having appreciable frictional engagement therewith, one of said members being adapted to be rotated through a plurality of revolutions, movement of the actuating member alongthe threaded shaft being adapted to operate the movable element; shoulder means on the nut providing a shoulder surface parallel to the axis of the member, movement of the actuating member along the threaded shaft being adapted to operate the switch means; shoulder means on each side of the nut; and cooperating shoulder means rigidly mounted on the threaded shaft at each end thereof, wherebyY the nut is caused to rotate with the threaded shaft, but without jamming thereon, at the desired limits of movement of the actuating member.

5. Apparatus of the characterclaimed in claim l, whereinthe actuating member includes means for readily adjusting said frictional engagement.

6. Apparatus of the character claimed in claim) 4, wherein the actuating member includes means for readily adjusting said frictional engagement.-

7. Apparatus of the character claimed in claim l, wherein the nut has annular flanges on each side thereof and the actuating member is rotatably mounted therebetween.

8. Apparatus of the character claimed in claim 4, wherein the switch means at one end. of the shaft comprises a single pair of contacts and tho switch means at the other end of the shaft provides -two pair ofA oppositely operating contacts,

one pair closing when the other opens and vice versa.

9. Apparatus of the character described for actuating' a movablev element, including: e

shaft; and cooperating shoulder means rigidly mounted on the threaded shaft providing a shoulder surface parallel to the axis of the shaft, whereby the nut is caused to rotate with the threaded shaft, but without jamming thereon, at the desired limits of movement of the actuating member. 5

10. Apparatus of the character. described for actuating a limit switch, including: a threaded shaft member adapted to be rotated through a plurality of revolutions; a nut on said shaft; an

actuating member rotatably mounted on said nut and having appreciable frictional engagement therewith: means preventing rotational but permitting axial movement of the actuating member, movement of the actuating member along the threaded shaft being adapted to operate the switch means; shoulder means on each side of the nut providing shoulder surfaces parallel to the airis,v of the shaft; and cooperating shoulder means rigidly mounted on the threaded shaft at each end thereof providing shoulder surfaces parallel to the axis of the shaft, whereby the nut is caused to rotate with the threaded shaft, but without jamming thereon, at the desired limits of movement of the actuating member.

11. Apparatus of the character claimed in claim 9, wherein the actuating member includes means for readily adjusting said frictional engagement.

RICHARD W. MAY.