Patent Abstract:
Data recording tape is passed along guides and past a read/write head. Sensors detect the position of the tape and adjust the guides and the head as a function of the position. If the tape deviates from the target tape path, a controller moves a guide to steer the tape back to the target tape path, using the sensor signals. In cases of tape disturbance such as those involving rapid tape motion, an adaptive estimator uses the sensor signals to position the head to anticipate the expected position of the tape when the disturbance arrives at the head.

Full Description:
TECHNICAL FIELD 
     This invention relates to equipment used in electronic media reading and writing, and more particularly to systems using data recording tape. 
     BACKGROUND 
     Tape read/write head assemblies include one or more read/write transducer heads positioned transverse to the intended path of a recording tape. The transducer heads write data on and read data from parallel tracks on the tape called “data tracks.” The head assembly can move laterally across the width of the tape to position a particular transducer head relative to a particular data track, with the head assembly&#39;s position controlled by a servo. 
     The tape itself may include tracks called “servo tracks,” which provide information to control the lateral position of the head assembly. Servo tracks serve as reference features or guide marks on the tape. By monitoring the position of the head assembly relative to the servo tracks, the head assembly can dynamically adjust the position of the transducer heads to keep the heads in a correct position relative to the tape tracks. Ideally, the tape path past the head assembly should not vary, but in practice lateral tape movement affects the position of a transducer head relative to a track. Dynamic repositioning is important because it compensates for the lateral movement. 
     In part because of servo control, data track widths have been made significantly narrower and the capacity of the recording medium has been increased. With a decrease of the width of data tracks and an increase of the number of tracks on a width of tape, servo control takes on added significance and greater precision is advantageous. The position of the transducer heads of the head assembly relative to tape tracks can become sensitive to a variety of disturbances, some of them minute. 
     Disturbances may arise, for example, from the equipment used to dispense the tape that is being fed past the transducer heads and from the equipment used to take up the tape after it had passed the transducer heads. In a typical case, for example, tape is dispensed from a first reel, which includes a hub and which often includes a flange, and is taken up by second reel. If a hub or a spindle supporting a reel is not perpendicular to the reel, the reel may wobble as it rotates. This wobble causes the tape to move laterally relative to the head assembly. 
     In addition, contact between the tape edge and the flange may produce lateral movement of the tape. When tape is taken up on a reel at high speed, for example, small pockets of air may become trapped between layers of tape, allowing one layer to slip laterally relative to another. Another potential source of lateral tape motion may come about due to the interaction between the head assembly and the tape. At times when the head assembly moves laterally relative to the tape to find a particular track, friction between the head assembly and the tape causes the tape to adhere to the head assembly and “follow” the head assembly. 
     Some of the lateral movements described above involve rapid changes in the lateral position of the tape relative to the head assembly, and other movements involve gradual changes. In the case where the tape follows the moving head assembly, for example, the initial tape movement may be gradual. There may come a point, however, at which the tension in the tape overcomes the frictional force, and the tape rapidly snaps back to a previous position. 
     SUMMARY 
     The invention provides systems that sense the lateral movement of data recording tape such as magnetic recording tape. One system monitors the tape position and adjusts the tape path based upon the tape position. Another system monitors the tape position and adjusts the position of the head assembly. The systems will be described separately, but typically the systems cooperate with each other to compensate for rapid (or “high-frequency”) changes and for more gradual (or “low-frequency”) changes in tape position. 
     In one embodiment, the present invention provides a system for positioning data recording tape. The system includes a sensor that detects the position of the tape and issues a position signal as a function of the tape position. The sensor may be, for example, an optical sensor or a magnetic sensor, and the signal may indicate how close the tape is to a target tape path. The system also includes a guide that interacts with the tape and a controller that moves the guide as a function of the position signal. By moving, the guide steers the tape. One technique for steering the tape with the guide is by tilting the guide. 
     In another embodiment, the present invention presents a system for positioning a head for reading and writing to data recording tape. The system includes a head, a sensor configured to detect the position of the tape and generate a signal as a function of the position, and a servo coupled to the head. The servo is configured to move the head as a function of the signal. Typically the sensor is located such that the sensor detects the tape&#39;s position before the tape passes the head. The system may also include an adaptive estimator, which receives the signal. Based upon the detected position or movement of the tape, the adaptive estimator may generate a second signal, which is used by the servo to move the head. With this system, the servo may move the head in anticipation of a disturbance that has not yet reached the head. 
     In a further embodiment, the present invention provides a method for steering data recording tape. The method includes passing the tape over a guide, sensing the position of the tape, generating a signal as a function of the position, and moving the guide as a function of the signal. 
     In still another embodiment, the present invention provides a method for moving the head in anticipation of tape disturbances. The method comprises detecting a disturbance in the path of the tape before the disturbance reaches the head, generating a signal as a function of the disturbance, and moving the head as a function of the signal. 
     In an additional embodiment, the present invention presents a system that includes a sensor that detects the position of data recording tape and issues a position signal as a function of the position of the tape. The system also includes a guide that interacts with the tape, a first controller that moves the guide as a function of the position signal, a head and a second controller that moves the head as a function of the position signal. The controllers may send signals to each other. 
     In a further embodiment, the present invention presents a control method. The method includes passing data recording tape over a guide and past a head. The position of the tape is sensed, and a position signal is generated as a function of the position of the tape. The method further includes moving the guide as a function of the position signal and moving the head as a function of the position signal. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagram of a tape guiding system. 
     FIG. 2 is a diagram of a movable tape guide. 
     FIG. 3 is a block diagram showing a feedback system. 
     FIG. 4 is a block diagram showing a feedback and feed forward system. 
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     FIG. 1 shows a system  10  that guides a tape  12  past a read/write head  18 . Tape  12  includes a lower edge  14  and an upper edge  16 . Tape  12  is dispensed from some apparatus such as a first reel (not shown in FIG.  1 ), and is taken up by other apparatus such as a second reel (not shown in FIG.  1 ). Tape  12  may travel past read/write head  18  from right to left or from left to right. When tape  12  is moving from left to right, tape  12  is dispensed and passes over a first guide  22 . Tape  12  then passes head  18 . Tape  12  passes over a second guide  26  before being taken up. 
     Head  18  moves up and down, allowing head  18  access to different tracks on tape  12 . The position of head  18  is governed by a head servo  20 , which is controlled by a servo controller (not shown in FIG.  1 ). In the example of FIG. 1, head  18  is a magnetic head that reads data from and writes data to tape  12 , which is magnetic recording tape. In other embodiments, however, head  18  and tape  12  may be arranged for optical recording. 
     Guides  22  and  26  stabilize tape  12  as tape  12  moves past head  18 , and guides  22  and  26  maintain tape  12  in or near the “target,” or desired, tape path. Guides  22  and  26  steer tape  12  in a manner to be described in more detail below. Guides  22  and  26  may be roller guides with smooth cylindrical surfaces and have a low coefficient of friction with tape  12 . Guides  22  and  26  may rotate about axes  24  and  28 , respectively. Alternatively, guides  22  and  26  may be fixed, with tape  12  sliding over the guides or tape  12  flying on entrained air over the guides. As shown in FIG. 1, guides  22  and  26  do not include flanges to guide tape edges  14  and  16 . Interaction between tape edge  14  or tape edge  16  and a flange tends to cause damage to the edge and affects the quality of the edge. Optionally, guides  22  and  26  could have flanges, with the flanges being removed from the tape path. The flanges would not serve to steer tape  12  during ordinary operation, but would serve as a safety feature to prevent tape  12  from slipping off guides  22  and  26  in rare cases of extreme tape movement. 
     Tape  12  may be housed, for example, in a tape cartridge. Some components of system  10 , including components described below, may be included in the tape cartridge. Alternatively, some components may be included in a tape drive that receives the cartridge and runs tape  12  past head  18 . Guides  22  and  26 , for example, may be mounted on a baseplate in the tape cartridge, or guides  22  and  26  may be mounted on a deck within the tape drive. The invention is intended to encompass system  10  without regard to whether its components are included in the cartridge, the driver, or any combination thereof. 
     Guides  22  and  26  are movable, with axes  24  and  28  being configured to change orientation. A first guide actuator  34  regulates the orientation of axis  24 , and consequently regulates the orientation of first guide  22 . Similarly, a second guide actuator  36  regulates the orientation of axis  28  and consequently regulates the orientation of second guide  28 . Guide actuators  34  and  36 , by regulating the orientation of guides  22  and  26 , can cause one or both guides to tilt relative to an axis substantially perpendicular to a tape drive deck across which tape  12  is moved. 
     Tilting of a guide changes the path of tape  12 , as illustrated in FIG.  2 . FIG. 2 shows first guide actuator  34  tilting axis  24  by an angle α to a tilted position  24 ′, causing guide  22  to move to a new position  22 ′. In the example in which guide  22  does not rotate, the tilting creates unequal longitudinal tension in tape  12 . Upper edge  16  is in greater tension than lower edge  14 . As tape  12  moves across guide  22 , tape  12  tends to slide downward on guide  22  to reduce the tension in upper edge  16 . By tilting guide  22  in an opposite direction, guide  22  places lower edge  14  in greater tension than upper edge  16 , thus steering tape  12  upward. In the example in which guide  22  rotates, steering techniques may differ. When tape  12  crosses a rotating guide, tape  12  may not necessarily move in a direction to decrease tension, and may be drawn in some circumstances in a direction that increases tension. Tape  12  may still be steered however by tilting guide  22 , but the tilting techniques may be different from the techniques employed when guide  22  is fixed. 
     The tilting shown in FIG. 2 is for purposes of illustration and is not intended to limit the invention. In FIG. 2, a tilt fulcrum  38 , where axes  24  and  24 ′ cross, is depicted near the bottom of guide  24 , but fulcrum  38  may be positioned at any other location, including a location other than one coincident with axes  24  or  24 ′. In addition, actuator  34  can be configured not only to tilt axis  24  of guide  22 , but also to translate guide  22  in one, two or three dimensions. For example, actuator  34  can move guide  22  downward, thus steering tape  12  downward. In addition, although FIG. 2 shows only first guide  22 , second guide  26  can be configured to move in a similar manner. 
     Returning to FIG. 1, sensors  30  and  32  are positioned between guides  24 ,  28  and the reels that dispense or take up tape  12 . Sensors  30  and  32  are shown monitoring upper edge  16  of tape  12 , but sensors  30  and  32  could also monitor lower edge  14 . Additional sensors may also be added, the additional sensors allowing upper edge  16  and lower edge  14  to be monitored simultaneously, for example, or monitoring edge positions between guides  24 ,  28  and head  18 . Sensors  30  and  32  may generate electrical signals indicative of the position of upper edge  16 . Sensors  30  and  32  may be optical sensors. Optical sensors offer good sensitivity and high accuracy, i.e., optical sensors are capable of monitoring upper edge  16  position very precisely. Furthermore, optical sensors also provide large bandwidth, i.e., optical sensors respond quickly to rapid changes in tape position. The invention is not limited to optical sensors, however. Sensors  30  and  32  may be other kinds of sensors, such as magnetic sensors configured to sense a magnetic track near the edge of tape  12 . 
     As will be described in more detail below, output signals from sensors  30  and  32  can be used by first guide servo  34  and second guide servo  36  to position first guide  22  and second guide  26 . Output signals from sensors  30  and  32  can be also used by head servo  20  to position read/write head  18 . 
     FIG. 3 is a block diagram illustrating a feedback system  40 . For illustrative purposes, it will be assumed that the system applies to edge sensor  30  and guide  22 . A tape position set point  42 , representing the ideal upper edge  16  position when tape  12  is aligned with the target tape path, is the input to feedback system  40 . The actual upper edge  16  position  50  is the output to feedback system  40 . The upper edge  16  position is sensed  48  by sensor  30 . The actual position  50  is subtracted  44  from the ideal position  42 , resulting in an error signal  52 . A guide controller that manages guide servo  34  steers tape  12  toward the target position, thus driving the error signal to zero. A similar feedback system may be employed with edge sensor  32  and guide  26 . 
     Steering of tape  12  by moving guide  22  or  26  generally cannot change the tape position quickly. For this reason, feedback system  40  tends to be more responsive to low-frequency changes in tape position and less responsive to high-frequency changes. A system that is better able to respond to high-frequency changes is shown in FIG.  4 . FIG. 4 is a block diagram illustrating a feedback/feed forward system  60 . Feedback/feed forward system  60  uses signals from sensors  30  and  32  to correct for read/write head  18  position errors and to anticipate movement of tape  12 . Although feedback/feed forward system  60  uses some common components as feedback system  40 , such as sensors  30  and  32 , the two systems  40  and  60  are shown as separate block diagrams for clarity. 
     Input to feedback/feed forward system  60  is the desired position of head  18  ( 62 ), relative to a point on tape  12 . The desired position of head  18  may be specified, for example, with respect to a particular data track or a particular servo track. Servo controller  72  places head  16  at a position relative to the tape ( 74 ). The actual head position relative to tape  12  ( 74 ) is negatively fed back ( 64 ) to correct for errors in the position of head  18 . The actual position ( 74 ), subtracted ( 64 ) from the desired position ( 62 ), produces an error signal ( 78 ), which is used by servo controller  72 . 
     Tape disturbance  70 , such as a high-frequency tape lateral motion, may affect the position of the head  18  with respect to tape  12  ( 74 ). Tape disturbance  70  also affects the position of tape  12  as detected by sensor  30  or  32  ( 68 ). Because many disturbances  70  are detected by sensors  30  or  32  before they reach head  18 , an adaptive estimator ( 66 ) may use sensor  68  signals to feed forward ( 64 ) signals to servo controller  72  to anticipate impending motion caused by tape disturbance  70 . As a result, servo controller  72  can position head  18  quickly when the disturbance reached head  18 , and can wholly or partially compensate for the disturbance when the disturbance reaches head  18 . 
     Adaptive estimator  66  may include, e.g., a differentiator to convert position signals from a sensor  68  to signals indicative of the velocity of tape movement. Adaptive estimator  66  may further include instructions or logic for recognizing tape disturbances caused by head  18  itself. For example, adaptive estimator may correlate tape position  68  with signals  76  from servo controller  72  to recognize cases in which friction between head  18  and tape  12  causes tape  12  to adhere to head  18  and follow head  18 . In such a case, adaptive estimator  66  may feed forward signals to counteract the feedback signals, thus keeping head  18  stationary. The advantage of counteracting is that it prevents head  18  from trying to pursue a track on tape  12  that friction prevents head  18  from reaching. 
     Although feedback system  40  and feedback/feed forward system  60  have been described separately above, and although systems  40  and  60  may operate alone or independently, it is usually advantageous for systems  40  and  60  to cooperate with each other. Cooperation allows improved compensation for high-frequency changes and low-frequency changes in tape position. For example, feedback system  40  may send a signal to feedback/feed forward system  60  that shows that feedback system  40  is steering tape  12  downward. Feedback/feed forward system  60  may use that signal to adjust the head position to follow the downward motion of tape  12 . 
     A number of embodiments of the invention have been described. These and other embodiments are within the scope of the following claims.

Technology Classification (CPC): 6