US 3608909 A
Description (OCR text may contain errors)
United States Patent Jacob Rabinow 6920 Selkirk Drive, Bethesda, Md. 20034 873,314
Nov. 3, 1969 Sept. 28, 1971 Inventor Appl. No. Filed Patented RECORD-FLATTENING TURNTABLE 4 Claims, 10 Drawing Figs.
U.S. Cl 274/39 ll, 248/362 1nt.Cl (1113/60 Field of Search 274/39,
References Cited UNITED STATES PATENTS Manwaring Aylsworth Kuhn Mallina Knight ct a1. ,1 Link Primary Examiner-Leonard Forman Assistant Examiner-Charles E. Phillips AllS'lRAC'I: A phonograph record turntuble is provided with means for flattening disc records placed thereon. Examples are shown for accomplishing this by means of vacuum or mechanical holddown devices.
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INVENTOR Jacob Robinow ATTORNEY RECORD-FLATTENING TURNTABLE Phonograph pickup cartridges are continually being improved by being made physically lighter and are capable of playing records with continually lower vertical pressures. Cartridges are available, at the present time, that can play records quite well with a vertical force of one-half gram, and it is anticipated that in the near future there will be cartridges to play records with a vertical force of about onetenth gram. When using such cartridges, it becomes important that some means be provided to play records which are normally not entirely flat, that is, which are warped or distorted in some manner. Records become distorted and warped both because of improper manufacture and because they are not stored under ideal conditions. They are made of plastic materials which deform under continuous stress and exposure to warm temperatures. When such a record is played on a conventional turntable, the cartridge is caused to move up and down due to warping, and since the cartridge has some mass, as it must have, if the vertical forces holding the cartridge down are very small, the cartridge may either jump out of the groove completely, or the relationship of the stylus relative to the cartridge changes rapidly, producing distortions of various types.
In modern stereo pickups, the angle between the stylus and the record is rather critical. In present-day practice, it is specified to be If the record is warped, the stylus angle changes rapidly, particularly because modern stylii have high compliances. The up-and-down motion of the record surface can produce Wow" both because the stylus angle is changed relative to the cartridge and because the whole arm is moved up and down. The pivots of most modern arms are above the surface of the record and this up-and-down motion produces the well-known wow effect. In order to minimize these effects, one should either obtain perfectly flat records, or else the records should be flattened when they are being played. The present invention discloses several methods of accomplishing this.
The specific nature of my invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings, in which:
FIG. 1 is a schematic drawing of a turntable using vacuum means to flatten a record;
FIG. 2 is a diametric cross-sectional view of the turntable shown in FIG. 1, but without the record;
FIG. 2A is a detail of the mechanism of FIG. 2;
FIG. 3 is a diametric cross-sectional view ofa turntable employing mechanical gravity holddown means for a record;
FIG. 4 is a view similar to FIG. 1, showing mechanical finger holddown means for a record;
FIG. 5 is a diametric sectional view of the arrangement shown in FIG. 4.
FIGS. 6-9 inclusive are detailed views showing various elements of the arrangement shown in FIGS. 4 and 5.
As shown in FIGS. 1 and 2, a turntable 2 is provided with circular grooves 3 connected to a central duct 4 which communicates with annular groove 6 in the fixed bearing 7 supporting the turntable. The turntable is shown as a flat platen of metal (or any other suitable material) mounted on a vertical shaft which rests on a ball inside a stationary bearing 7. The turntable can be driven by a belt 8 which in turn is driven by a suitable motor 9, or it can be driven by a friction idler 8 as shown in FIG. 3. The method of driving the turntable is not part of this invention. Annular groove 6 communicates with exhaust duct 6a.
Mounted on the turntable 2 is a rubber platen 11 shown in section in FIG. 2. This member is a sheet of rubber or rubberlike material which has its outer edge molded so as to be normally raised as shown at 12, and the inner edge raised as shown at 13. The raised section can be feather-edged as shown in FIG. 2A at 12'. The rubber is, of course, provided with circular openings which communicate with the annular grooves 3 and which communicate with the vacuum system described below. The rubber used is quite soft and pliable so as to conform to the record when it is first laid on the turntable, and
thus to seal the vacuum space and permit the vacuum to perform its function. When the record is placed on the turn table, the outer edge of the rubber touches the record near its outer periphery, just beyond the playing grooves, while the inner edge contacts the area generally reserved for the label.
When the vacuum is turned on simultaneously with the turning on of the turntable motor by switch 5, the area under the record will be evacuated and air pressure will force the record to lie flat against the turntable as shown in FIG. l. The pump 16 and motor I7 driving it are conventional and can be of any suitable type. Obviously, if it is to be located near the turntable it should be as small and quiet as possible, and it should be suitably enclosed in box to eliminate the possibility of noise being transmitted directly to the outside air. This is particularly so if the record player is to be played in homes; in studio use, the noise of the pump and motor may be of small consequence. FIG. 1 shows a vacuum-operated switch 14 which is used to shut off the pump motor when the vacuum reaches a predetermined value. In order to minimize fluctuations in the vacuum line 611, a storage tank 18 is provided which is connected to this vacuum line. If the seal between the record and the flexible platen Jill is good, very little pumping action is necessary after the initial pulldown of the record. The vacuum-controlled switch 14 acts to shut off the motor when this is the case. As the vacuum drops due to the inevitable leakage under the record and through the bearings, the switch 14 closes and the motor 17 again pumps down the system.
Another method of automatically adjusting the action of the vacuum pump is to use a pump motor that develops its maximum torque at zero speed or at very low speed. Such motors are known in the trade as torque motors. They are not injured by low speed operation down to stall. Such a motor, then, would run fast and quickly evacuate the space under the record and, as the record flattens out on the turntable and the quantity of air pump is reduced, the motor would slow down. This reduces the wear on the motor and pump and reduces the noise generated by these two devices.
It should be understood that suitable shaft seals can be used at the top of the bearing to reduce the leakage and minimize the entrance of dust at this point. With the above system, it will be apparent that all the user has to do is to place the record on the turntable in the customary manner and operate the starting switch 5, the holddown action being entirely automatic.
FIG. 3 shows a mechanical method of flattening warped records, which is very simple and inexpensive, but is not as convenient to use as the vacuum system. In this case the record is placed on the turntable which, again, can be driven by any suitable means such as motor 9' driving an idler 8 which, in turn, drives the turntable. The idler can, of course, be on the inside or outside of the turntable as is customary in current practice. A weighted ring 21 made of metal such as brass or zinc is slipped over the record after it is placed on the turntable. The ring is centered by the outside surface of the turntable so as not to disturb the balance of the turntable. The undercut and the holddown flange 22 of the ring is made large enough to accept the normal variations in the outside diameters of records. The turntable is beveled at 23 so as to enable easy removal of the record by exposing the record edge to enable the operator to grip the edge easily.
FIG. 4 shows a more elaborate and more automatic means of holding the record down by means of mechanical fingers which grip the record during the playing cycle, or only during the vacuum pulldown cycle, if desired. The action of the tingers can best be understood by examining FIG. 5. The turntable 25 consists of the usual flat plate supported by central shaft 27 and bearing 28 in the conventional manner. The turntable can be driven by a belt or friction idler as explained above. For the sake of clarity, the motor drive is shown in FIG. 4 but not in FIG. 5.
Passing through a multiplicity of openings 26a in the periphery of the turntable are fingers 29 which are hinged at the lower extremities to cross arm levers 30. These levers are in turn hinged at their centers on downwardly projecting posts 32 which are integral with or attached to the underside of the turntable 25. The inner ends of these levers 30 are resting under the flange 33 of spoollike members 34. The spoollike member is free to slide up and down on the cylindrical projection 36 cast integrally with the turntable 25, or attached separately thereto.
Each of the levers 30 is provided with torsion spring 37 driving the member into the position shown in FIG. 5, that is, the left-hand member 30 is driven counterclockwise by the spring 37. The lever is pivoted to the holddown finger 29 and a very light torsion spring 38 is provided about the pivot pin 39 driving the finger relative to the lever in a clockwise direction so as to move the holddown finger toward the record. Reference is made to FIGS. 7, 8 and 9, which show the successive positions of these holddown fingers as will be described later. The spool 34 can be. moved down against the action of the pivot springs 37 and 38 by a fork 41 shown in FIGS. and 6. The fingers of the fork 41 rest against the bottom flange of the spool member as shown in FIG. 6. The whole fork is pivoted at 42 and the pivot is attached rigidly to the fixed baseboard of the machine. The fork can be actuated manually by means of eccentric 43 operating through a metal link 44 or directly by an electrical solenoid, pneumatic cylinder, or any other suitable mechanism. The eccentric 43 can also be turned by a motor or the link 44 can be actuated by a cam. The exact method of moving the fork is not important. A manually operated eccentric is shown for the sake of simplicity. When the eccentric 43 is rotated so as to lift the line 44, the fork rotates clockwise so that its two fingers 46 push down on the flange 35 and swing the levers 30 into the downward or open position of the holddown fingers. By way of example, the operation of the left-hand lever 30 will be examined in more detail. FIG. 5 shows the lever 30 in its normal playing position. As the lever swings clockwise, its left-hand end moves up, lifting the holddown finger 29 up from the turntable as shown in FIG. 7. As the lever continues to move up the bottom leg of the rotary finger touches the top of the opening 26a of the turntable 26 and begins to swing out as shown in FIG. 8. As the lever continues to rotate clockwise, moved by the downward motion of the spool, the finger finally reaches its position shown in FIG. 9, which is the completely open condition of the holddown device.
In FIG. 5, a switch 48 is operated by an insulating block 49 attached to the link member 44. As this link member moved up to open the turntable, it also opens the circuit of the driving motor (FIG. 4). The turntable will normally continue to coast because of its inertia. The fork fingers not only act to pull down the spool 34, but will also act as brakes on the turntable and cause it to come to a stop. Other means of decelerating the turntable are well known in the art and need not be shown here.
The dimensions of the flange are such that the forked fingers 46 do not tough the flange 35 during normal playing of the records; that is, they rest slightly above the maximum vertical position of the flange 35 so as not to produce any noise or undesirable friction on the turntable.
When the turntable finally comes to a stop, the operator merely has to lift the record off the turntable and replace it with another. At this time, he will move the eccentric 43 to the position shown in FIG. 5, permitting the spool 35 to move to its upper position as shown in FIG. 5, and the sequence of finger positions will be reversed, as shown in FIGS. 9, 8 and 7, in that order. The springs on the lever 30 will always act to pull the fingers in and because of the relationship of the hinge points 39 relative to the edge of the record 20, the resulting forces will not only pull the record down but will also pull the fingers in against the edge of the record.
In the above device, there must, of course, be provision to prevent the stylus from hitting the tips of the fingers. To accomplish this, a fixed guard 51 is shown attached to the baseboard 52 and positioned so that the edge of the guard is just above the other edge of the record 20. If the guard is properly positioned and proportioned, the cartridge can never be swung to a position where it can hit the fingers 29. This guard can also be used as a guide for lowering the cartridge and its arm in a manual record player. In automatic record players, where the arm position is determined by other means,
the guard may be unnecessary, but it is advisable just as a form of insurance so that if the cartridge-lowering mechanism should fail, absolute protection will be provided against the stylus hitting the revolving fingers 29.
The number of fingers 29 depends on engineering choice. For use with ordinarily warped records, it appears that six fingers are sufficient and that a vertical travel of about a quarter of an inch is enough for ordinary cases. Of course, in' the special case of a badly warped record, one could increase considerably the magnitude of the motions and increase the number of fingers, but it is also possible to initially flatten the record by hand and hold it down until the fingers close in. Although manual means are shown for opening and closing the fingers and starting and stopping the vacuum, etc., in automatic record players these functions would be accomplished by a mechanism coupled to the record-changing mechanism so that the starting and stopping of the motor of the vacuum pump, the opening and closing of the fingers, etc. would be done by suitable linkages connected to the rest of the mechanism.
While the mechanical means to pulldown the outer edge of the record, shown in FIGS. 3 and 4, may be sufficient to flatten records that are only slightly warped, these mechanical means can be used in conjunction with badly warped records to assist the vacuum mechanism or to act merely at the beginning of the vacuum cycle to effect the initial vacuum seal for the vacuum pulldown. In FIG. 5 are shown vacuum ducts which are essentially the same as those in FIG. 2. The action of starting a record-playing cycle would be similar to that described for the vacuum system alone except that the pulldown fingers 29 would be used at the beginning to effect an initial seal with the vacuum taking over the main duty of holding the record flat.
It should be noted that with a well fitting center spindle, so special seals are needed at the center of the record for initial pulldown. In any case, such an inner-lip seal is shown at 13 in FIG. 2.
It will be understood that the invention is not limited to the exact embodiment shown and that various modifications can be made in construction and arrangement within the scope of the invention.
a. A turntable for phonograph disc records having means to flatten a record on said turntable during the playing cycle,
b. said flattening means comprising a number of peripherally spaced mechanical finger means pivotally attached to the underside of the turntable and arranged to hook over the outer edge of a disc record, and to pull the rim of the record down against the turntable during playing of the record.
2. The invention according to claim 1,
c. means to actuate said fingers so as to move them up from the disc and out from the edge of the disc when releasing the record, and in toward the disc and down onto the disc when playing.
3. The invention according to claim 1,
c. and additional vacuum means to reduce the pressure under a record on said turntable.
a. A turntable for phonograph disc records having means to flatten a record on said turntable during the playing cycle,
b. said flattening means comprising a number of peripherally spaced mechanical finger means attached to the turntable to pull the rim of the record down against the turntable during playing of the record,
c. means to actuatesaid fingers so as to move them up from the disc and out from the edge of the disc when releasing gage a portion of the turntable so that as the outer end of the lever moves in one direction, the finger is disengaged from the record and as the outer end moves in the other direction, the finger is engaged with the record,
g. yoke means engageable with a flange on said collar to control vertical movement of the collar and through it of said levers,
f. stationary mounted mechanical linkage means controlling the movement of said yoke moans.