Abstract:
Tape recording and playback apparatus ( 10 ) including tape head cleaning assembly ( 80-92 ) for intermittent cleaning of one or more tape head(s) mounted in the periphery ( 18 ) of a helical scanning drum ( 12 ) forming part of the apparatus ( 10 ). Loading of a cassette ( 24 ) carrying the tape, extension of the tape ( 20 ) by movable guides ( 44,46 ) into contact with the drum periphery ( 18 ), and movement of a pinch roller ( 50 ) are controlled by a motor-driven cam ( 40 ) as described in EP0782136-A1. Instead of also using the prior art cam to control tape tension, this is now done by dynamic braking of the motor ( 30 ) for the tape supply reel ( 26 ). In accordance with the invention, the fourth control function of the prior art cam is now utilised for selective mechanical actuation of a swinging arm ( 82 ) on which is mounted an abrasive cleaning wheel ( 80 ). Rotation of the control cam ( 40 ) to its “fourth function” position allows the arm ( 82 ) to pivot and thus brings the abrasive wheel ( 80 ) into temporary contact with the periphery ( 18 ) of the helical scanning drum ( 12 ) so as to remove debris clogging the tape head(s). High performance of the data recording/playback unit ( 10 ) is maintained by the inventive adaptation of existing hardware ( 40 ) to effect intermittent operation of a tape head cleaner ( 80 ) built-in to the unit ( 10 ).

Description:
FIELD OF THE INVENTION 
     This invention relates to tape recording and playback apparatus, and relates more particularly but not exclusively to the intermittent cleaning of helical scanning drums utilised in tape recording and playback apparatus. 
     DESCRIPTION OF PRIOR ART 
     It is well known to utilise magnetic tape for recording and replaying high frequency signals that may represent (for example) video pictures or computer data (i.e., analogue data, digital data, or a mixture of analogue and digital data). Such magnetic tape is commonly held on and extends between two rotatable reels normally housed within a tape cassette. A form of electromagnetic transducer known as a tape head is utilised for writing signals onto magnetic tape (“write” operation) or for reading previously recorded signals (“read” operation). Both read and write operations require relative movement between the magnetic tape and the tape head, and the greater the bandwidth requirements (i.e. the greater the highest signal frequency to be dealt with), the greater must be such relative velocity. For directly recorded audio-frequency signals (e.g. music) it is sufficient for the tape head(s) to be stationary, and for the tape to be wound past the tape head(s) at a mechanically undemanding velocity. However, for writing and reading signals of a much higher frequency, e.g. video signals and computer data signals, it is known to mount one or several tape heads in the periphery of a drum which is rotated about a central axis that is skewed with respect to a notional perpendicular through the plane of tape movement such as to give the tape head(s) a component of movement transverse to the length of the tape (which passes along a path that extends around part of the periphery of the rotating drum), as well as giving the tape head(s) a component of movement along the tape. Such relative movement is known as “helical scanning” while the combination of tape head(s) and rotating drum is known as a “helical scanning drum”. 
     On the one hand, high-frequency data signals require a very high fidelity of writing and reading if interference and other errors are to be avoided, but on the other hand, the high velocity rubbing contact between tape and tape heads tends to result in the accumulation of scraped-off magnetic recording medium and/or other debris (e.g., airborne dust and dirt) on the tape heads. Such accumulations of debris degrade the performance of the tape heads, and must be avoided, or removed before worsening performance reaches an unacceptable level. Continuous cleaning of the periphery of a helical scanning drum is likely to cause excessive friction and wear, and/or to be ineffective if contact pressure of the cleaner on the drum is reduced in an attempt to avoid excessive friction and wear. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided tape recording and playback apparatus including a cleaning assembly having a cleaning means operable to clean the periphery of a helical scanning drum of said apparatus by contact therewith, the cleaning means being mounted for controllable movement into and out of contact with the periphery of the helical scanning drum, the assembly further comprising contact control means coupled to the cleaning means for controlling movement of the cleaning means into contact with the periphery of the helical scanning drum, the contact control means comprising a cam means including a cam-driving motor and a motor-driven cam, said cam means being operable to displace the cleaning means to make contact with the periphery of the helical scanning drum, said motor being a multi-function motor additionally utilisable for one or more of the additional functions of motor-driven loading of a tape cassette holding a length of magnetic tape, dragging a length of tape from the cassette into contact with the periphery of the helical scanning drum, and moving a pinch roller to pinch a portion of the tape against a tape-driving capstan forming part of the apparatus, such movements being effected by mechanisms coupled with the motor-driven cam, characterised in that said cam means is operable to displace the cleaning means independently of said additional functions. 
     Preferably said cam means is arranged to operate intermittently to cause the cleaning means to make intermittent contact with the periphery of the helical scanning drum. 
     The cleaning means may be mounted on movable mounting means comprising an arm or a bracket which is rotatable and/or slidable and which also comprises a cam follower co-operating with the cam means to be controllably moved thereby. The cam-driving motor is preferably a rotary electric motor having a rotatable output shaft, and the motor-driven cam is preferably a rotary cam directly connected to the rotatable output shaft of the cam-driving motor to be directly rotated thereby in use of the cleaning assembly. 
     The cleaning means is preferably an abrasive cleaning means operable to clean the periphery of the helical scanning drum by a combination of physical contact therewith and relative movement therebetween in use of the cleaning assembly. The abrasive cleaning means is preferably an abrasive wheel mounted for free rotation about a wheel axis in use of the cleaning assembly. 
     According to a second aspect of the present invention there is provided a method of operating apparatus according to the first aspect of the present invention, the method comprising the steps of controlling movement of the cleaning means into contact with the periphery of the helical scanning drum upon each occurrence of a selected one or more of the following conditions: 
     (a) upon the loading and/or unloading of a tape cassette; 
     (b) at substantially regular intervals of time; 
     (c) upon a data error being detected during a write cycle and/or during a read cycle; 
     (d) upon receipt of a manually originated command signal. 
     Preferably, movement of the cleaning means is such as to effect temporary or intermittent contact with the helical scanning drum. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawing, the sole FIGURE of which is a schematic representation of relevant parts of a preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drawing is a simplified and highly schematic diagram of mechanical and electromechanical parts of the preferred embodiment; electronics related to data writing and data reading are omitted for the sake of clarity, and because they are not immediately relevant to the invention. As used below, the term “apparatus” refers to a tape recording and playback apparatus for writing data onto magnetic tape and reading data from magnetic tape, the data being digital data, analogue data, or a mixture of digital and analogue data. 
     Referring to the drawing, a tape recording and playback apparatus  10  has a helical scanning drum  12  rotatable by an electric motor  14  via a mechanical drive  16 . The drum  12  has one or more tape heads (not shown) mounted in the periphery  18  of the drum  12  to read and/or write data or other signals from and/or to magnetic tape  20  held against and wrapped part-way around the drum periphery  18 . The helical scanning drum  12  and its drive  14  and  16  are of known form, with the drum  12  being rotated during read/write operation by the motor  14  via the mechanical drive  16 , the drum  12  rotating about an central drum axis  22  which is skewed slightly away from right angles to the notional plane occupied by the portion of the tape  20  wrapped around the drum periphery  18 , such that the tape head(s) scan the peripherally-wrapped portion of the tape  20  with a movement that includes both longitudinal and transverse components, i.e. a form of scanning known as “helical scanning”. 
     The magnetic tape  20  is supplied from and returned to a tape cassette  24  of known form within which are mounted a rotatable supply reel  26  and a rotatable take-up reel  28 . The supply reel  26  is driven or dynamically braked by an electric motor  30  via a mechanical drive  32 . The take-up reel  28  is driven or dynamically braked by an electric motor  34  via a mechanical drive  36 . (Alternatively, the take-up reel  28  can be a permanent part of the apparatus  10 , with the tape  20  being supplied in a one-reel cartridge (not shown), the apparatus  10  comprising means (not shown) of known form to pull a tape leader from the cartridge to the take-up reel  28 ). 
     When the tape cassette  24  is first loaded into the apparatus  10 , the reels  26  and  28  are uncoupled from their respective drives  32  and  36 , and magnetic tape  20  initially extends between the reels  26  and  28  along a path (not depicted) not projecting beyond the outline of the cassette housing. Loading of the cassette  24  initiates (e.g. by means of a microswitch, not shown) the pulling of the cassette  24  within the tape apparatus  10  and engagement of the reels  26  and  28  with their respective drives  32  and  36 , the appropriate cassette movements being effected by a first mechanical linkage  38  actuated by a motor-driven cam  40  which will be detailed subsequently. Next, the cam  40  operates a second mechanical linkage  42  to cause a pair of movable tape guides  44  and  46  to hook the tape  20  between the reels  26  and  28  from its initial position entirely within the cassette  24  and, by suitable movement of the guides  44  and  46 , to extend the inter-reel portion of the tape  20  until the tape  20  is wrapped part-way around the drum periphery  18 . Finally, the cam  40  operates a third mechanical linkage  48  to cause a pinch roller  50  to pinch the newly extended tape  20  against the periphery of a tape-driving capstan  52  driven by a capstan motor  54  via a mechanical drive  56 . The magnetic tape  20  is now ready to be written onto and/or read from by means of the tape head(s) in the periphery  18  of the helical scanning drum  12 . 
     In the drawing, the motor-driven cam  40  is schematically depicted as a rotary cam bi-directionally rotated by a cam-driving motor  58  via a mechanical drive  60 . The first, second and third mechanical linkages  38 ,  42  and  48  couple to respective cam tracks  62 ,  64  and  66  formed on the cam  40  (these cam tracks being depicted in the drawing as simple circles rather than the mechanically complex shapes referred to below). 
     The various motors  14 ,  30 ,  34 ,  54  and  58  are operated by and under the control of a control unit  68  which internally incorporates a controllable power supply (not depicted separately) that supplies controlled power to requisite ones of the motors (via respective power connections  70 ,  72 ,  74 ,  76  and  78 ) in a manner to cause each motor to operate as and when required (as may be ascertained from the operational description given subsequently). 
     Other than for certain differences which will be detailed subsequently, the structure and operation of the cam  40  and of its associated cam-actuated mechanisms are as described in published European Patent Application EP0782136-A1 (wherein the equivalent cam is coincidentally referenced “ 40 ”) the contents of which being incorporated herein by reference. 
     It is to be particularly noted that the cam motor in EP0782136-A1 is a multi-function motor which serves (through the intermediary of the cam  40  and its associated mechanisms) for cassette loading, tape loading, pinch roller actuation, and reel brake actuation (referred to as “pressing force varying”) for controlled variation of back tension in the tape. From the description of the latter function (see columns 5-16 of EP0782136-A1), it will be seen that the latter function is independent of the first three functions. This functional independence is preserved in the adaptation of the cam and cam motor of EP0782136-A1 to the present invention, as will subsequently be detailed. 
     Whereas EP0782136-A1 was concerned with use of its cam to control the tension of tape being payed-out from its tape supply reel, in the present invention tape tension is controlled by controlled dynamic braking of the respective reel motor. Specifically, when tape is being payed-out from the supply reel  26  to be scanned by the drum  12  and taken up on the reel  28  driven by the motor  34  during normal operation of the apparatus  10 , tension in the tape  20  between the cassette  24  and the drum  12  is controlled by suitable energisation of the motor  30  as determined by the combined control unit/power supply  68 , in a manner to cause the motor  30  to provide an appropriate level of dynamic braking through a combination of reverse torque (or drag) and forward motion (i.e. rotation of the motor  30  allowing the reel  26  to turn clockwise as depicted in the drawing so that tape feeds from the reel  26  to the drum  12  via the guide  44 ). Should tape tension require to be controlled during reverse motion of the tape  20 , the motor  34  would be energised to provide dynamic braking. 
     Since tape tension is controlled in the present invention by the tape reel motors, this frees the cam system adapted from EP0782136-A1 from its previous requirement to provide controlled reel braking to achieve tape tension, and allows the freed-up cam function to operate the drum cleaning system which will now be detailed. 
     The means by which the periphery  18  of the helical scanning drum  12  is cleaned is an abrasive wheel  80  which is rotatably mounted on an arm  82  which is, in turn, pivotally mounted on a pivot  84  anchored at a suitable location inside the apparatus  10 . The wheel  80  is formed as a freely rotatable hub having several flaps of abrasive-coated fabric (e.g. emery cloth) each attached at one edge to the periphery of the hub so as to be carried round by rotation of the hub but otherwise to have free movement radially in and out from the hub. The arm  82  is pivotally biased by a spring  86  having one end  88  bearing against the arm  82  and the other end  90  anchored against a suitable fixed location inside the apparatus  10 . The spring  86  is disposed in a manner to bias the arm  82  in a direction which tends to pivot the arm  82  such as to bring the abrasive wheel  80  against the drum periphery  18 . However, the abrasive wheel  80  is normally held out of all direct contact with any part of the drum  12  by means of a cam follower  92  mounted on the arm  82  and bearing against the cam  40  such that the interaction of the cam  40  and the cam follower  92  hold the arm  82 , against the bias of the spring  86 , in a pivoted position in which the wheel  80  is entirely clear of the drum  12 . 
     The form of the cam follower  92  and of the co-operating parts of the cam  40  can take any suitable form, and are shown by way of example with the cam follower  92  as a wheel which is rotatably mounted on a free end of the arm  82 , the wheel  92  bearing against the periphery of the rotatable cam  40  which is circular apart from a reduced-radius portion  94  about to be described. 
     Operation of the previously referred-to mechanisms by which the cassette  24  is loaded, the tape  20  is hooked and guided against the drum  12 , and the tape  20  is pinched against the capstan  52  by movement of the pinch roller  50 , is caused by rotational interaction of the cam tracks  62 ,  64  and  66  with the linkage mechanisms  38 ,  42  and  48  as previously described and as more fully detailed in EP0782136-A1. Such interaction is brought about by suitable rotation of the cam  40  (as driven by the motor  58  under the control of the control unit  68 ), and corresponds to the rotational cam positions “40-1”, “40-2”, and “40-3” illustrated in FIG. 4 of EP0782136-A1. In the present invention, such rotational cam positions keep the reduced-radius portion  94  of the periphery of the cam  40  away from the cam follower  92 , and maintain the cam follower  92  against the constant-radius portion of the cam periphery such that the abrasive wheel  80  is held away from the drum periphery  18 . 
     When it is desired to clean the tape head(s) by means of contact of the abrasive wheel  80  with the drum periphery  18  (wherein the tape head(s) is/are mounted), the cam  40  is controllably rotated to bring the reduced-radius portion  94  angularly into alignment with the cam follower  92 . This allows the cam follower  92  to reduce its radial separation from the rotational centre of the cam  40 , so allowing the spring  86  to pivot the arm  82  about the pivot  84  (in a clockwise direction as depicted in the drawing) and thus to allow the abrasive wheel  80  to swing into contact with the periphery  18  of the helical scanning drum  12 . (The rotational position of the cam  40  now corresponds to the rotational position “40-4” shown in FIG. 4 of EP0782136-A1, except that instead of the prior art function of tape tensioning, the different function of tape head cleaning is now being controlled by the cam). 
     During the cleaning process, rotation of the helical scanning drum  12  is maintained by suitable energisation of the drum motor  14  from the control unit/power supply  68 , such that the drum  12  rotates past the abrasive wheel  80  at the same time as the drum periphery is in physical contact with the wheel  80 . Thus the rotating drum  12  tends to spin the abrasive wheel  80 . Abrasive cleaning of the drum periphery  18  may be enhanced by a transverse scrubbing component of relative motion if the rotational axis  81  of the abrasive wheel  80  is suitably skewed with respect to the drum axis  22 . 
     After a suitable interval (e.g. a few seconds), the cam  40  is again rotated (onwards or in reverse as deemed suitable) such as angularly to displace the reduced-radius portion  94  away from the cam follower  92  and to bring the constant-radius portions of the periphery of the cam  40  back under the cam follower  92 , so forcing the arm  82  to pivot (anti-clockwise as depicted in the drawing) against the biasing force of the spring  86  thus to lift the abrasive wheel  80  out of contact with the periphery  18  of the helical scanning drum  12  and so terminate the tape head cleaning cycle. 
     Performance of the tape head cleaning cycle can be arranged to occur at suitable intervals, preferably such as to ensure a minimum standard of tape head cleanliness (freedom from clogging) without subjecting the tape head(s) to excessive abrasion. Cleaning can be arranged to occur automatically upon each occasion that a tape cassette is loaded into the apparatus, or at suitable regular intervals of time, or upon the detection of (or upon the suspicion of) degraded tape head performance (e.g. as signified by the occurrence of a data read/write error), or upon any selected combination of such occasions. Additionally or alternatively, tape head cleaning can be initiated by a manual control signal. 
     The arm  82  which mounts the cleaning wheel  80  and the cam follower  92  is schematically depicted in the drawing as a straight arm with a fulcrum located between the ends of the arms. In practical embodiments, the arm may have any suitable shape which suitably disposes arm-mounted components, and the arm may be slidable as well as or instead of being pivotable. The spring  86  is depicted as an example only of means to bias the cleaning wheel  80  out of contact with the helical scanning drum except during cleaning, but actual biasing means can take any suitable form, e.g. a torsion spring (not shown) acting on the arm  82  at its pivot  84 . Any suitable form of cleaning means can be employed in place of the wheel  80 , e.g. a brush or the like, which may be non-rotatable. 
     Modifications and variations of the above-described embodiments can be adopted without departing from the scope of the invention as defined in the appended claims. For example, in the present embodiment, while there is a multi-function motor responsible for the additional functions of cassette loading, tape loading, and pinch roller actuation, it will be appreciated that the multi-function motor may in practice be responsible for more functions, or a subset of these additional functions.