US3660740A

US3660740A - Device for remote-control operation of knobs in television receivers or the like

Info

Publication number: US3660740A
Application number: US58419A
Authority: US
Inventors: Gerhard Rossteutscher
Original assignee: August Schwer Soehne GmbH; SABA GmbH
Current assignee: August Schwer Soehne GmbH; SABA GmbH
Priority date: 1969-07-25
Filing date: 1970-07-27
Publication date: 1972-05-02
Anticipated expiration: 1989-05-02
Also published as: DE1937750A1; CA918452A; DE1937750B2; DE1937750C3

Abstract

A device for actuating by remote control a row of pushbuttons in a television or radio receiver wherein a mechanism automatically releases a previously actuated pushbutton in response to actuation of another pushbutton. The device has a series of parallel slides each coupled to one of the pushbuttons, a feed screw which can be driven stepwise in clockwise and counterclockwise directions, and a follower which meshes with and moves lengthwise of the feed screw when the latter rotates. The slides have coplanar projections and the follower has two angularly and axially offset cams one of which engages successive projections in front of it to actuate the respective pushbuttons in response to rotation of the feed screw in one direction and the other of which engages successive projections in front of it to actuate the respective pushbuttons in response to rotation of the feed screw in the other direction. The follower is pivoted in response to changes in the direction of rotation of the feed screw to place the one or the other cam into the plane of the projections and the follower comes to rest in such positions that it cannot interfere with manual actuation of the pushbuttons.

Description

United States Patent Rossteutscher May 2, 197 2 (54] DEVICE FOR REMOTE-CONTROL OPERATION OF KNOBS [N Primary Examiner-Bernard A. Gilheany TELEVISION RECEIVERS OR THE Assistant ExaminerW. E. Duncanaon, Jr. LIKE Attorney-Michael S. Striker 72 Inventor: Gerhard Rossteutscher, Villingen, Ger- 1 ABSTRACT many A device for actuating by remote control a row of pushbuttons 3 Assign; Saba Schwarzwnmer ApparateJhwAm in a television or radio receiver wherein a mechanism autosm", August schwer s m Gmb. v m matically releases a previously actuated pushbutton in gen Germany response to actuation of another pushbutton. The device has a series of parallel slides each coupled to one of the pushbutl l Filed: y 1970 tons, a feed screw which can be driven stepwise in clockwise [2H Appl- No: 58.419 and counterclockwise directions, and a follower which meshes with and moves lengthwise of the feed screw when the latter rotates. The slides have coplanar projections and the follower (30] Foreign Applicati n Prior ty Da a has two angularly and axially offset cams one ofwhich engages July 25 969 Germany g P 19 37 7505 successive projections in front of it to actuate the respective pushbuttons in response to rotation of the feed screw in one [52] Us. CL 318/265, 318/467 direction and the other of which engages successive projec- [511 lnLCL llllllllll tions in front of t to actuate the respective pushbuttons in [58] Field 0' Search 318/265 266 466 467 response to rotation of the feed screw in the other direction The follower is pivoted in response to changes in the direction [56] References Cited of rotation of the feed screw to place the one or the other cam into the plane of the projections and the follower comes to rest UNITED STATES PATENTS in such positions that it cannot interfere with manual actuation of the pushbuttonsi 2,295,355 9/1942 Prescott ..3I8/266 945,472 [/1910 Mooresnm ..3l8/266 l5Claims,5 Drawing Figures 23 ll lllllllllllllll MU Llj/ Pahntod May 2, 1972 3,660,740

I Shun-Shut 1 Patented May 2, 1972 3,660,740

2 Shuts-Shut 2 DEVICE FOR REMOTE-CONTROL OPERATION OF KNOBS IN TELEVISION RECEIVERS OR TIIE LIKE BACKGROUND OF THE INVENTION The present invention relates to improvements in devices for adjusting radio receivers, television receivers or other apparatus by remote control. For example, the device of the present invention can be used for selection of channels in a television receiver, for selection of stations in a radio receiver, and/or for precision tuning of such apparatus. Still more particularly, the invention relates to improvements in devices for remote-control actuation of pushbuttons, levers, knobs or like manually actuatable adjusting elements which enables the operator to actuate a selected element by remote control or by hand.

It is already known to provide a television receiver or a radio receiver with a set of pushbuttons each of which is actuatable to select a particular channel or station. It is also known to provide such apparatus with a device for actuation of the knobs by remote control, for example, from a chair. Presently known remote-control devices normally comprise an electric motor or an electromagnet which rotates the shaft of the channel selector. Certain other known devices employ discrete electromagnets, one for each knob. All such constructions are quite complicated, expensive prone to malfunction, bulky and not sufficiently versatile to permit rapid selection of any desired channel or station.

German Utility Model No. 1,997,770 discloses a device which permits cyclical actuation of knobs in a predetermined sequence. Each following knob is "prepared" in response to depression of the preceding knob, and a single electromagnet is employed to insure actuation of the knobs in the predetermined sequence. A drawback of such proposal is that it often takes very long if the user wishes to select a particular channel or station when the corresponding knob is ahead of the knob which was actuated before. For example, if the operator has actuated the knob No. 3 of a series of nine knobs and, thereupon wishes to actuate the knob No. 2, the knobs Nos. 4, 5, 6, 7, 8, 9, l must be actuated prior to actuation of the knob No. 2. This is a time-consuming operation and the wear on the moving parts is quite pronounced.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved remote-control device for actuation of several knobs or like adjusting elements in any desired sequence, with little loss in time and without interfering with manual actuation of the knobs when the remote-control device is not in use.

Another object of the invention is to provide a remote-control device which can be built into or combined with existing television receivers, radio receivers or analogous apparatus.

A further object of the invention is to provide a remote-control device whose versatility far exceeds the versatility of conventional devices, which occupies little room, and which can be used for actuation of relatively few or for actuation of substantial numbers of knobs or like adjusting elements.

An additional object of the invention is to provide a device which permits cyclical or anticyclical operation of a series of adjusting elements and wherein the time required for anticyclical actuation of such elements is but a small fraction of the time which is required for analogous operation in presently known devices.

The invention is embodied in a structure which can be incorporated in or combined with a television or radio receiver and comprises a row or series of knobs, pushbuttons, levers or analogous adjusting elements which are actuatable by hand or by remote control to move from an idle to an operative position, a release mechanism for moving to the idle position a previously actuated element in response to actuation of another element, and a novel remote-control device for selectively actuating the adjusting elements. The remote-control device comprises a plurality of slides or analogous motionreceiving members each of which is connected with one ofthe adjusting elements and is movable between first and second positions respectively corresponding to operative and idle positions of the respective adjusting element, a rotary feed screw which preferably extends at right angles to the directions of movement of the motion-receiving members, drive means for rotating the feed screw in clockwise and counterclockwise directions, and follower means meshing with the feed screw and arranged to move along the feed screw in first and second directions in response to clockwise and counterclockwise rotation of the feed screw. The motion-receiving members are located in the path of movement of and are movable to first positions by the follower means. Return movement of such motion-receiving members to second positions is effected by the aforementioned mechanism which automatically returns a previously actuated adjusting element to idle position in response to actuation of another adjusting element.

In order to reduce the time which is necessary for actuation of a selected adjusting element, the follower means comprises two discrete motion transmitting portions in the form of cams or the like one of which can move to first positions those motion-receiving members which are located in front of the one cam when the follower means travels in one direction and the other of which can move to first positions those motionreceiving members which are located in front of the other cam while the follower means travels in the other direction. The follower means is preferably pivotable on the feed screw between two end positions in one of which the motion-receiving members are coplanar with one cam and in the other of which the motion'receiving members are coplanar with the other cam. The follower means is movable stepwise through such distances that it comes to a halt in positions in which it cannot interfere with manual actuation of selected adjusting elements.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved remote-control device itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a plan view of a remote-control device for three adjusting elements which embodies the present invention;

FIG. 2 illustrates a portion of the structure shown in FIG. 1 with the follower located in a different position;

FIG. 3 shows the structure of FIG. 2 with the follower in a third position;

FIG. 4 is a transverse sectional view as seen in the direction ofarrows from the line IV-IV of FIG. I; and

FIG. 5 is a sectional view as seen in the direction of arrows from the line VV of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I, there is shown a housing 1 which supports a row of adjusting elements here shown as pushbuttons or knobs 2, 3 and 4. Each of these knobs can be depressed by hand to thereby select a particular channel in a television receiver. The housing I further contains a conventional releasing or resetting mechanism which automatically releases a previously depressed knob in response to depression of another knob. For example, if the knob 2 was depressed by the viewer of the television receiver to select a first channel and the viewer thereupon wishes to switch over to a second channel, the knob 3 or 4 is depressed whereby the knob 2 is released and automatically returns to its normal extended position. The knobs 2-4 are also rotatable, either by hand or by remote control in a manner known per se to thereby adjust the sharpness of the picture and/or the quality of sound. The exact construction of the release mechanism which is installed in the housing 1 to release a previously depressed knob in response to depression of a fresh knob and to simultaneously retain the fresh knob in depressed position forms not part of the present invention. Reference may be had, for example, to German printed publication No. l,246,091 published Aug. 3, 1967 which shows a mechanism capable of holding in depressed position only one of several knobs at a time and which also illustrates and describes the manner in which the rotation of a depressed knob brings about a change in the resistance of an associated potentiometer which can be used for accurate tuning of a diode.

The present invention relates to a novel device for automatically depressing or actuating a selected one of the knobs 2, 3, 4 by remote control and in any desired sequence. For the sake of simplicity, the drawing shows that the housing 1 is provided with only three knobs but it will be readily understood that the number of knobs or analogous adjusting elements may be increased and multiplied without departing from the spirit of the invention. Shortly outlined, the invention resides in the provision of a remote control device which enables the opera tor to effect depression or actuation of any selected knob, for example, the knob 3, thereupon the knob 4, again the knob 3, then the knob 2, thereupon the knob 4, and so on whereby the switching from one channel to any other channel, either cyclically or anticyclically, consumes little time. At the same time, the improved device does not prevent manual actuation of any desired knob.

Referring again to FIG. 1, the knobs 2, 3, 4 are respectively connected with pull rods 5, 6, 7 which are articulately con nected by pins 8, 9, 10 with motion-receiving members or

slides

11, 12, 13. Thus, when a selected knob is depressed by hand, the associated rod pushes the corresponding slide in a direction to the left, as viewed in FIG. 1 whereby such slide remains in the left-hand end position until the operator decides to actuate another knob, either by hand or by remote control. The slides are parallel to and equidistant from each other and are reciprocable in the side walls 14a ofa trough 14 whose end walls 14b support spaced portions of a rotary feed screw or spindle 15 meshing with an internally threaded follower 17. The feed screw 15 can be rotated by a drive including a small DC motor 16 of reversible polarity. Thus, the motor 16 can cause the follower 17 to move back and forth lengthwise of and along the spindle 15 whereby the follower can effect actuation of a selected knob by way of the associated

slide

11, 12 or 13. It is assumed in H6. 1 that the motor 16 drives the feed screw 15 in a direction to move the follower 17 downwardly whereby a first wedge-like motion transmitting portion or cam 22 of the follower engages the tip of a complementary wedge-like motion-receiving projection or portion 19 of the slide 12; thus, the follower 17 has moved the knob 3 to its depressed position whereby the aforementioned release mechanism in the housing 1 automatically releases the previously depressed knob 2 or 4 and at the same time releasably holds the knob 3 in depressed position. The cam 22 of the follower 17 is flanked by two

edge faces

22a, 22b which make an obtuse angle. A second motion transmitting portion or cam 21 of the follower 17 is flanked by edge faces 21a, 21b and this second cam is angularly offset with reference to the cam 22 through an acute angle of between 20 and 40 (see FIG, 4). The wedge-

like projections

18, 19, 20 of the

slides

11, 12, 13 are located in a common plane and the follower 17 can pivot on the feed screw 15 to such an extent that is places its

cam

21 or 22 into the plane of the projections 18-20. As stated before, FIG. 1 shows the cam 22 in engagement with the tip of the projection 19 on the slide 12 for the median knob 3; therefore, the cam 21 is located above the common plane of the projections 18-20.

in accordance with a feature of the invention, the control means for the motor 16 is designed in such a way that the motor automatically rotates the feed screw 15 through a predetermined number of revolutions until the follower 17 assumes a position (see FIG. 2) in which it does not interfere with manual depression of a selected knob. Thus, after having shifted the median slide 12 to the extent necessary to effect deeper penetration of the knob 3 into and its retention in the housing 1, the follower 17 has continued to move toward the motor 16 to place the tip of its cam 22 into the gap between the

projections

19 and 20. in this way, the cam 22 permits depression of the knob 2 or 4. The cam 21 cannot interfere with the actuation of knobs because it is located outside of the plane of the projections 18 to 20.

The control means for automatically arresting the motor 16 when the follower 17 assumes a position in which it cannot interfere with manual actuation of the knobs 2-4 comprises a disk 25 (see FIGSv 1 and 5) which is driven by the motor 16 through a transmission including spur gears 23, 24 at such a rate that the follower 17 covers a distance 0 whenever the disk 25 completes a full revolution. The distance 0 corresponds to the distance between the tips of the projections 18-19 or 19-20. The disk 25 has a peripheral notch 29 for one arm ofa two-armed lever 26 which is pivotable on a shaft 260 and whose other arm closes one of two

switches

27, 28 whenever the one arm is not received in the notch 29. The means for selecting the direction of rotation of the feed screw 15 comprises two selector knobs $0, 51 one of which is depressed when the operator wishes the follower to travel toward a first limit switch 33 and the other of which is depressed when the operator wishes to move the follower toward a second limit switch 32. The

switches

27, 28, 32, 33 are installed in the circuit of the motor 16 in such a way that the motor is arrested when the

switches

27, 28 are open at the same time and that the motor is arrested when the follower 17 actuates the limit switch 32 or 33. The angular position of the notch 29 in the periphery of the disk 25 is selected with a view to insure that the

switches

27, 28 open simultaneously when the tip of the

cam

21 or 22 is out of register with the tip ofone of the

projections

18, 19, 20; this insures that the operator can depress any one of the knobs 2, 3,, 4 when the motor 16 is at a standstill.

The knobs 50, 5] can be activated by hand or by remote control.

FIG. 2 illustrates the follower 17 at a standstill after the cam 22 has moved the slide 12 for the median knob 3 to the lefthand end position. The cam 22 of the follower 17 has advanced beyond the tip of the projection 19 and dwells in an intermediate position in the gap between the

projections

19 and 20. The operator can now elect to actuate the knob 4 or to actuate the knob 2, i.e., the knobs can be actuated cyclically in the sequence 2, 3, 4 or anticyclically in the sequence 4, 3, 2). Another feature of the invention resides in the provision of means for changing the angular position of the follower 17 on the feed screw 15 whenever the follower is to change the direction of its movement, i.e., from a first direction in which the knobs 2, 3, 4 are operated in the just given sequence to a second direction in which the knobs are actuated anticyclically. Such change in angular position of the follower 17 brings about the advantage that the interval for actuating the knob 2 following actuation of the knob 3 is less than in presently known devices. Were the means for moving the follower 17 constructed in the conventional manner, actuation of the knob 2 subsequent to actuation of the knob 3 would have to be preceded by actuation of the knob 4. Thus, and referring again to FIG. 2, the outer edge face 22a of the cam 22 would first shift the projection 20 to its left-hand end position and the follower would thereupon change the direction of its movement to actuate with its edge face 22b the knob 3 prior to actuating the knob 2. The means for changing the angular position of the follower 17 on the feed screw 15 becomes effective in automatic response to depression of the knob 51 which starts the motor 16 in such a way that the feed screw transports the follower toward the limit switch 32. Such means includes an arm 17a which is rigid with the follower 17 and extends radially of the feed screw 15 (see 110. 4), a motion transmitting yoke 31 which extends into a V-shaped recess 17b of the arm 17a and is parallel with the feed screw 15, and a friction clutch 30 which is mounted on the feed screw and one element of which is connected with the adjacent portion of the yoke 31. The extent of angular displacement of the follower 17 is indicated by the angle alpha; such angular displacement suffices to insure that the follower can pivot between two end positions 1 and 11 in one of which the cam 32 is located in the common plane of the projections l8-20 and in the other of which the cam 21 replaces the cam 22 in such plane. The yoke 31 does not interfere with movement of the follower 17 lengthwise of the feed screw 15 but it invariably changes the angular position of the follower when the direction of rotation of the feed screw is changed by the motor 16 in response to depression of the knob 50 or 51. Stops 34, 35 are provided to prevent angular movements of the yoke 31 and follower 17 about the axis of the feed screw 15 beyond the aforementioned end positions.

If the operator wishes to effect actuation of the knob 2 following actuation of the knob 3 (while the follower 17 dwells in the position shown in FIG. 2), the knob 51 is depressed to start the motor 16 whereby the motor rotates the feed screw 15 in a direction to move the follower l7 upwardly, as viewed in FIG. 2. At the same time, the friction clutch 30 pivots the yoke 31 which in turn pivots the follower 17 clockwise, as viewed in FIG. 4, to move the cam 21 into the plane of the projections 18-20. The cam 21 then enters such plane in the gap between the

projections

18 and 19 and its outer edge face 21a engages the projection 18 to thereby move the knob 2 to the depressed position (see FIG. 3). Thus, the motor 16 is merely required to move the follower 17 through a single distance a to thereby cause the cam 22 to bypass the projection 19 and to cause displacement of the slide 11 by way of the cam 21. It will be noted that the improved device is capable of actuating the knob 2 following the actuation of knob 3 within an interval of time which is just as short as the interval required to actuate the knob 4 following the actuation of knob 3. As explained above, the presently known devices operate in such a way that the knobs must be actuated cyclically before the first knob of the series is to be actuated whereby such procedure consumes much more time than the selection of channels by resorting to the just described device. The inner edge faces 21b, 22b do not come into engagement with the

projections

18, 19 and 20 so that they can be configurated in any desired way as long as they do not interfere with manual actuation of the knobs 2, 3, 4 when the follower 17 is at a standstill.

The motor 16 is automatically arrested when the follower 17 trips the limit switch 32 or 33. These switches are positioned in such a way that the switch 33 is actuated when the follower 17 moves downwardly from the position shown in FIG. 2 through a single distance a and that the switch 32 is ac tuated when the follower moves upwardly from the position of FIG. 2 through the distance 2a. The knob 50 or 51 must be depressed more than once if the operator wishes to move the follower 17 through a multiple of the distance 0. Whenever the follower 17 is at a standstill, its

cam

21 or 22 is located in the gap between the projections 18-19 or 19-20 or is outwardly adjacent to the

projection

18 or 20.

It is clear that the invention can be embodied with equal advantage in radio receivers or any other apparatus wherein a row of knobs or analogous adjusting elements is to be actuated by hand as well as by remote control and where it is desirable to actuate the adjusting elements in any desired sequence as well as to permit manual actuation of selected elements when the remote-control device is idle.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

lclaim:

l. A structure of the character indicated comprising a plurality of movable adjusting elements, particularly pushbuttons or knobs, each actuatable by hand as well as by remote control to move from an idle to an operative position and each arranged to move from said operative to said idle position in response to actuation of another element; and a remote control device for selectively actuating said elements and comprising a plurality of motion-receiving members each connected with one of said elements and each movable between first and second positions respectively corresponding to operative and idle positions of the associated elements, a feed screw, drive means for rotating said feed screw in two directions. and follower means meshing with said feed screw and arranged to move therealong in first and second directions in response to clockwise and counterclockwise rotation of the feed screw, said motion-receiving members being located in the path of and being movable to first positions by said follower means.

2. A structure as defined in claim 1, wherein said motionreceiving members comprise coplanar motion-receiving portions and are movable in parallelism with each other, said feed screw being at least substantially normal to the directions of movement of said motion-receiving members.

3. A structure as defined in claim 1, wherein said follower means comprises two motion transmitting portions one of which moves to first positions those motion-receiving members which are located ahead of such one portion when the feed screw is rotated in one direction and the other of which moves to first positions those motion-receiving members which are located ahead of such other portion when the feed screw rotated in the other direction.

4. A structure as defined in claim 3, wherein said-motion receiving members comprise coplanar wedge-shaped projections and each portion of said follower means constitutes a wedge-shaped cam, each of said cams being bounded by two mutually inclined edge faces.

5. A structure as defined in claim 4, wherein said edge faces include two outer edge faces one of which engages and moves successive projections during rotation of the feed screw in said one direction and the other of which engages and moves successive projections during rotation of the feed screw in said other direction.

6. A structure as defined in claim 5, wherein one of said cams is angularly offset with reference to the other cam.

7. A structure as defined in claim 6, wherein said follower means is pivotable about the axis of said feed screw between two end positions in one of which said projections are coplanar with one of said cams and in the other of which said projections are coplanar with the other cam.

8. A structure as defined in claim 7, wherein said follower means is pivotable through an angle of 20-40.

9. A structure as defined in claim 1, wherein said drive means is arranged to rotate said feed screw stepwise through such distances that the follower means is disengaged from said motion-receiving members and permits manual actuation of said elements whenever said feed screw is at a standstill.

10. A structure as defined in claim 1, wherein said motionreceiving members are parallel to each other and said feed screw extends at right angles to said members, said members having coplanar projections and said follower means comprising a first cam arranged to move to first positions successive projections located in front of said first cam during rotation of said feed screw in one direction and a second cam arranged to move to first positions successive projections located in front of said second cam during rotation of said feed screw in the other direction, said follower means being pivotable on said feed screw between a first position in which said first cam is coplanar with said projections and a second position in which said second cam is coplanar with said projections, and further comprising means for pivoting said follower means between said positions in response to changes in the direction of said feed screw.

H. A structure as defined in claim 10, wherein said means for pivoting the follower means comprises a friction clutch provided on said feed screw and motion transmitting means connecting said clutch means with said follower means.

12. A structure as defined in claim 1, wherein said drive means comprises a reversible-polarity electric motor and selector means for starting said motor in the desired direction.

13. A structure as defined in claim 12, wherein said follower means is movable lengthwise of said feed screw between two end positions and further comprising a pair of switches in circuit with said motor and each actuated by said follower means in one of said end positions to hereby arrest said motor.

14. A structure as defined in claim I, wherein said drive means comprises an electric motor and control means for automatically arresting said motor in response to a predetermined number of revolutions of said feed screw.

15. A structure as defined in claim 14, wherein said number of revolutions corresponds to lengthwise movement of said follower means through a predetermined distance so that the follower means comes to a standstill always in a position in which said elements are actuatable by hand.

I! 1 Q i 1

Claims

1. A structure of the character indicated comprising a plurality of movable adjusting elements, particularly pushbuttons or knobs, each actuatable by hand as well as by remote control to move from an idle to an operative position and each arranged to move from said operative to said idle position in response to actuation of another element; and a remote control device for selectively actuating said elements and comprising a plurality of motionreceiving members each connected with one of said elements and each movable between first and second positions respectively corresponding to operative and idle positions of the associated elements, a feed screw, drive means for rotating said feed screw in two directions, and follower means meshing with said feed screw and arranged to move therealong in first and second directions in response to clockwise and counterclockwise rotation of the feed screw, said motion-receiving members being located in the path of and being movable to first positions by said follower means.

2. A structure as defined in claim 1, wherein said motion-receiving members comprise coplanar motion-receiviNg portions and are movable in parallelism with each other, said feed screw being at least substantially normal to the directions of movement of said motion-receiving members.

8. A structure as defined in claim 7, wherein said follower means is pivotable through an angle of 20*-40*.

10. A structure as defined in claim 1, wherein said motion-receiving members are parallel to each other and said feed screw extends at right angles to said members, said members having coplanar projections and said follower means comprising a first cam arranged to move to first positions successive projections located in front of said first cam during rotation of said feed screw in one direction and a second cam arranged to move to first positions successive projections located in front of said second cam during rotation of said feed screw in the other direction, said follower means being pivotable on said feed screw between a first position in which said first cam is coplanar with said projections and a second position in which said second cam is coplanar with said projections, and further comprising means for pivoting said follower means between said positions in response to changes in the direction of said feed screw.

11. A structure as defined in claim 10, wherein said means for pivoting the follower means comprises a friction clutch provided on said feed screw and motion transmitting means connecting said clutch means with said follower means.

14. A structure as defined in claim 1, wherein said drive means comprises an electric motor and control means for automatically arresting said motor in response to a predetermined number of revolutions of said feed screw.