1. Field of the Invention
The present invention relates generally to the field of office dictation equipment, and more particularly to a drive mechanism for a miniaturized, portable, hand held dictating machine.
Office dictation equipment has been in widespread use for well over half a century, and various types of office dictation equipment are found in most offices where any substantial volume of various forms of information is dictated and must be transcribed and typed. Although dictation equipment has under gone many changes over the years, one aspect of such equipment which has remained fairly constant is the size and arrangement of the equipment and the manner in which it is normally maintained in the office for use. Typically, a dictating machine is a unit in the order of 8 to 10 inches square and 3 to 4 inches high and rests upon the desk or credenza of the user in a position convenient to where the user sits so that he can hold a suitable microphone adjacent to his mouth, the microphone being connected to the dictating machine by a wire. Various media have been employed for recording the user's voice, among those being cylinders and disks on which a groove is cut much like that on a conventional phonograph record, or a wide plastic belt on which a groove is cut, a wide magnetic belt on which the user's voice is recorded by means of a magnetic track, and more recently magnetic tape which is fed from a supply reel to a take up reel, as is well known in the tape recording art, or which is stored in cassettes which have become well known in connection with portable cassette recorder and play back devices.
During the past several years, a rather remarkable change as occurred in the development of dictation equipment which has resulted from miniaturization of both the electronic components which are conventionally part of modern dictation equipment as well as tape cassettes used therewith. It became apparent to both technical and business people in the dictation equipment field that it would be highly desirable if an entire dictating machine could be reduced to the size of what has long been the size of just the microphone unit of a typical desk top dictating machine. It was also recognized that the advantages of such a dictating machine would be quite substantial in that the user of the dictating machine would no longer be confined to the area of his desk or other place where the dictating machine is normally maintained, nor would he be put to the inconvenience of moving a relatively heavy and bulky piece of equipment if he wished to use the dictating machine in a location different from that in which it was normally maintained. Accordingly, a large variety of miniaturized, hand held dictating machines soon appeared on the market which, while having individual differences with respect to appearance, controls and functions, all had one thing in common, which was that they were small enough to be conveniently held in one hand during operation. These dictating machines averaged in size about 6 inches long by 3 inches wide by an inch thick, were battery powered and would record the user's voice on magnetic tape stored in a cassette and included sufficient self contained components to provide for instant rewind and play back of the recording on the tape. As is well known to anyone who has investigated this type of product, the market for portable hand held dictating machines has seen enormous growth and success, and many major domestic and foreign electronic and office machine companies are competing with each other in the production and marketing of this product.
As has been the case in many other fields of electronic products, modern technological developments in miniature electronic components has facilitated the design and development of consistently smaller dictating machines. The development of miniature microphones, miniature transducers for recording on and playing back from the magnetic tape, various electronic components utilized in any form of sound recording or reproducing apparatus and miniature speakers have all contributed significantly to the technology of miniaturizing dictating machines. One major problem which has been encountered and which has proven to be very difficult to solve in connection with the design of small dictating machines is the miniaturization of the mechanical components which are necessary in order to move the recording member past the transducer, or the record/play back head, as it is sometimes referred to. It was not until the development of the magnetic tape cassette that miniaturization of dictating machines was even contemplated in view of the fact that the earlier forms of recording media, that is disks or wide belts, did not lend themselves to miniaturization However, magnetic tape in cassette form has been developed in which the tape is extremely thin, in the order of 9 microns and relatively narrow in the order of 2 mm, and this has made possible the development of dictating machines in which a cassette can be used which is not much larger than a commemorative-type postage stamp and on which as much as 30 minutes of recording time is possible. However, the mechanical components necessary to drive the tape from the cassette to a recording or play-back position and back into the cassette are extremely difficult to miniaturize for a number of reasons. One of these reasons is that as mechanical parts are made smaller, they become weaker and cannot take the strain that would normally be imposed upon them in the course of operation to perform their intended functions. A second reason is the difficulty encountered in designing small parts which have limited strength capability so that they will inter-fit and function properly when a substantial amount of movement of these parts is required as is the case in the dictating machines. Still another reason is the problem of utilizing the limited amount of power which is available from a battery source to drive small capacity motors to accomplish the same overall mechanical operation as is accomplished in desk top dictating machines with substantially greater sources of power and larger capacity motors. These problems have resulted in a large amount of design and development in the miniaturized dictating machine field directed toward finding solutions to these problems, of which the foregoing are not all inclusive. While many of these problems have been solved to a substantial extent by developments in the prior art, some problems have not been adequately solved and some additional problems have been created by the solutions already proposed which themselves create the need for further development. Thus, there still remains considerable need for further technological developments in miniaturized dictating machines, particularly in connection with a desire to further reduce the overall size of these machines to enhance the portability and the convenience of use thereof.
In most forms of audio recording and play-back equipment which use magnetic tape, there are two forms of drive for moving the tape from one reel to another past the recording and play-back transducer. The mechanically simpler of the two is the so-called tape reel drive, in which one of the tape storage reels in the cassette is driven so as to wind tape on the driven reel while simultaneously unwinding it from the other reel which would normally be in an idling condition. Under normal circumstances, all of the tape in a cassette would be stored on a supply reel except for a leader portion which would be connected to a take-up reel in order to permit the tape to be wound thereon when the cassette is inserted into the recording machine. In order to avoid unnecessary complication and expense, the take-up reel is driven at a constant angular velocity. A major disadvantage of this type of system is that the tape can never be moved past the recording transducer at a constant linear velocity, and this introduces a number of problems. One of these is that the tape cannot be efficiently utilized in terms of recording time since the linear velocity of the tape commences from a predetermined minimum and increases from that point. The reason for this is that the linear velocity of the tape gradually increases as the diameter of the tape stored on the take up reel increases since the take up reel is being driven at a constant angular velocity. In order to maintain flutter at a minimum acceptable level, it is necessary to feed the tape past the recording transducer at a certain minimum linear velocity, which depends largely on certain characteristics of the tape. Clearly, satisfactory audio reproduction would be accomplished if this minimum velocity could be maintained over the entire length of the tape. However, since the linear velocity of the tape is gradually increasing over its entire length, the entire tape is being fed at a velocity that is more than necessary to maintain the desired minimum level of flutter of the recording. Thus, the length of tape in the cassette is being moved past the transducer in a considerably shorter period of time than what would otherwise be necessary if the tape were being moved at a constant linear velocity, and this of course reduces the amount of recording time on the given length of tape. Another disadvantage of the reel drive arrangement is that the uniformity with which the tape is fed past the transducer is dependent upon variations in the quality of the tape since the tape is literally being pulled from the supply reel by the take up reel and is thereby subjected to physical stresses which can result in slight variations in movement past the transducer. Since these variations may not be reproduced in the transcribing equipment, the result will be a pronounced difference in the frequency of the reproduced signal and this will cause undesirable variations in the quality of the audio reproduction.
The foregoing disadvantages are overcome by use of the so-called capstan drive. In this arrangement, a capstan is mounted in the recording machine immediately adjacent to the transducer, and a back up or pressure roller assembly is provided so as to press the tape into feeding relationship with the drive capstan. The pressure roller is moveably mounted so that it can be disengaged from the drive capstan when it is desired to stop the feeding of the tape. In order to prevent slack tape from building up between the drive capstan and the tape up reel in the cassette, another drive is provided for the cassette take up reel which rotates the reel at an angular velocity fast enough to wind the tape upon the reel when the reel is empty at the same linear velocity at which the tape is being fed by the drive capstan. Typically, a slip clutch is provided so that as the tape builds up on the take up reel, the reel can rotate at a gradually slower angular velocity even though the drive to the take up reel is maintained at a constant velocity. A principal advantage of the drive capstan feeding arrangement is that the recording time for a given length of tape is maximized because the tape is fed past the transducer at a constant linear velocity. Another advantage of the drive capstan arrangement is that it affords excellent control over the feeding of the tape past the transducer, particularly in that it permits the tape to be fed past the transducer at an extremely uniform linear velocity, thereby greatly reducing any tendency toward audio distortion resulting from variations in the movement of the tape past the transducer. Also, since the drive capstan is typically mounted as close as possible to the transducer, there is very little likelihood that the physical characteristics of the tape will in any way effect the uniformity of linear velocity of the tape past the transducer.
There are however certain problems which arise in connection with capstan drive tape feeding assemblies. One of these is that the capstan must be driven with an extremely uniform rate of angular velocity in order to achieve a uniform linear velocity of the tape. Since the drive capstan is typically a very small diameter element having very little mass and therefore highly subject to minute inertial changes, the drive input to the capstan must be very accurate. A second problem is that not only must the drive capstan be driven but also the tape reel must be driven, as well as the mechanism for moving the pressure roller into contact with the capstan to drive the tape, all of which means that a greater number of parts must be driven in this type of system than in the tape reel drive system described above. Hence, a larger power input is needed, typically in the form of a larger drive motor.
These problems in miniaturized capstan drive feeding systems have been relatively easily solved in prior art audio recording and play back equipment where size limitations have not been a major problem in connection with the design of drive components. However, these problems are greatly magnified, and their solutions made much more difficult, in the environment of miniaturized hand held dictating machines. As will be seen in more detail hereinafter, it has proven much more difficult to provide highly stable, uniform velocity capstan drive mechanisms in the miniaturized form which these mechanisms must take in order to be physically compatible with the limited dimensions of a miniaturized hand held dictating machine.
2. Description of the Prior Art
One type of miniaturized capstan drive tape feeding system is illustrated in U.S. Pat. No. 4,305,103, in which, as best seen in FIG. 4 thereof, a motor 24 drives a motor pulley 90 which in turn drives a flywheel 96 having a rubber tire 98 thereon, a drive capstan 36 being coaxial with the fly wheel 96 and being driven thereby. A pinch roller 38 is brought into contact with the capstan 36 by a suitable mechanism when it is desired to feed tape. A drive gear 92 is also mounted coaxially with the capstan 36 and drives an intermediate gear 94 which in turn drives the reel gears 74 and 174 which are mounted on the reel shafts 62 and 162. The reel shafts 62 and 162 drive the cassette reels through suitable one way and slip clutches in order to facilitate winding and rewinding of the tape between the tape reels. One of the major disadvantages of this type of drive is the large amount of space that is required for the flywheel 96 so that it will provide the necessary inertia to maintain a uniform angular velocity of the capstan 36. It can be seen in FIG. 1 that the flywheel occupies substantially the entire width of the dictating machine and, if it were desired to make the dictating machine narrower than that shown in FIG. 1, the flywheel would obviously have to be of a smaller diameter, and this would result in inertia being sacrificed. Another disadvantage is that a relatively slow speed motor must be utilized because there is only a one speed reduction stage between the motor and the drive capstan, that being the reduction between the diameter of the pulley 90 and the diameter of the flywheel 96. Since it is more difficult to maintain slow speed motors at a constant rate of speed than high speed motors, a certain degree of inaccuracy of the drive system is introduced right at the motor.
Another form of capstan drive tape feed arrangement is that shown in U.S. Pat. No. 4,134,145 in which it is seen that a motor has a drive pulley which drives a belt connected to a second driven pulley which is mounted coaxially with the drive capstan. Another pulley mounted coaxially with the drive capstan drives another belt which in turn drives a pair of pulleys mounted coaxially with the drive shafts for the tape reels of the cassette. Although this type of drive arrangement eliminates the necessity for the extremely large flywheel shown in the '103 patent, it has the disadvantages of not having a sufficient amount of mass in the system to provide sufficient inertial force to stabilize the drive chain and to maintain a constant linear velocity of the tape, and it also necessitates the use of a relatively slow speed motor because of the fact that there is only one stage of speed reduction between the pulley on the motor and the pulley on the drive capstan. Thus, it is seen, that a truly satisfactory capstan drive tape feeding arrangement has not been provided prior to the present invention for use in a miniaturized hand held dictating machine.