GB2349266A

GB2349266A - Tape transport mechanism with tape path deviation sensor

Info

Publication number: GB2349266A
Application number: GB9908988A
Authority: GB
Inventors: Nicholas James Roberts; Dean Anthony Edward Miles; Douglas Spencer Payne
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1999-04-21
Filing date: 1999-04-21
Publication date: 2000-10-25
Also published as: GB9908988D0

Abstract

A device for detecting deviation of tape path in a tape transport mechanism, comprises a tape contact sensor (30) with an external contact surface (34) and sensing means (40,41) for detecting a gap (52) between the contact surface (34) and tape (14) moving in a longitudinal direction across the contact surface (34), a processor means (46), an output (44) from the sensor (30) that provides to the processor means (46) at least one signal representative of a detected gap (52) between the contact surface (34) and the tape (14), the processor (46) being responsive to changes in the output signal in order to deactivate (50) a tape transport mechanism in the event of a detected gap (52), in which the contact surface (34) has in the longitudinal direction a convex shape over which moving tape may slide, the convex shape including a median portion (36) and longitudinally adjacent this a measurement portion (38), wherein the sensing means (40,41) is capable of detecting separation between a moving tape and the measurement portion (38) when moving tape (14) remains in contact with the median portion (36).

Description

Tape Transport Mechanism with Tape Path Deviation Sensor The present invention relates to an apparatus and a method for detecting deviation of tape path in a tape transport mechanism.

Magnetic or optical tapes are used in a wide variety of data storage and information recording applications. Such tapes are bound into reels for storage and such reels may be open reels or housed within a cartridge or cassette having both supply and take up reels. A tape transport mechanism is therefore required to move the tape along a tape transport path between the supply and take up reels.

Normally, the tape has to be moved at a controlled speed for data or information to be recorded or read from the tape. In many systems, a pinch roller arrangement is provided near a read/write head to more accurately control the movement of the tape. The pinch roller arrangement may comprise a driven capstan spindle roller and an idler roller coated with an elastomeric material that presses the tape against the capstan spindle. In order to control the movement of the tape, the pinch roller arrangement is usually upstream of the read/write head. It is known, however, to have more than one such pinch roller arrangement in a tape path, for example in an audio cassette tape mechanism having auto-reverse.

Because of the popularity of the compact audio cassette tape format, tapes and tape players are often used in hostile environments, particularly in motor vehicle passenger compartments where temperatures in summer may exceed 45 C. Tape transport mechanisms are usually quite reliable, but tapes can suffer under heat and humidity owing to degradation of the tape base or binders or lubricants in the magnetic coating. If a tape becomes tacky, then it can begin to adhere to the idler roller and begin to wrap itself around this roller. This usually results in destruction of the tape and possibly also damage to the tape transport mechanism. Often, the tape player may need to be removed for servicing in order to disentangle the tape.

Another way in which tape can start to wrap around a roller is if the take-up tape tension is lost, which can happen owing to excessive friction in a take up reel.

It is an object of the present invention to provide a convenient apparatus and method for detecting the start of this process before a tape becomes entangled around a roller.

Accordingly, the invention provides a device for detecting deviation of tape path in a tape transport mechanism, comprising a tape contact sensor with an external contact surface and sensing means for detecting a gap between the contact surface and tape moving in a longitudinal direction across the contact surface, a processor means, an output from the sensor that provides to the processor means at least one signal representative of a detected gap between the contact surface and the tape, the processor being responsive to changes in the output signal in order to deactivate a tape transport mechanism in the event of a detected gap, in which the contact surface has in the longitudinal direction a convex shape over which moving tape may slide, the convex shape including a median portion and longitudinally adjacent this a measurement portion, wherein the sensing means is capable of detecting separation between a moving tape and the measurement portion when moving tape remains in contact with the median portion.

In the case of a tape transport mechanism loaded with a tape, comprising a tape supply reel, a tape take up reel, means to move the tape under tension along a tape path from the supply reel to the take up reel, and a pinch roller arrangement in the tape path to control the tape movement, the device according to the invention should be provided upstream of the pinch roller arrangement. It is then possible to arrange the device in the tape path so that when tape starts to wrap itself around a roller, the tape path in the vicinity of the tape contact sensor will change to open up a gap between the tape and the measurement portion of the curved surface. The processor means can then act swiftly to stop movement of the tape before the tape becomes wound around the roller, or before it becomes impossible for the tape transport mechanism to reverse the tape motion to unwind the tape about the roller.

In a preferred embodiment of the invention, the contact surface has in the transverse direction a flat or a convex shape. A convex shape may be desirable in order to help centre the tape on the contact surface.

In order to improve the accuracy of the measurement, it may be desirable if the sensing means has two transducers for detecting the same physical property of moving tape, one transducer being arranged to detect the physical property in the median portion, and the other transducer being arranged to detect the physical property in the measurement portion, the at least one output signal being representative of the detected property in the median and measurement portions.

The gap may be measured in any of a different number of ways. For example, the sensing means may include at least one magnetic transducer for detecting the magnetisation of moving tape. This technique would rely on there being prerecorded magnetic information on the tape. The sensor then would act in the manner analogous to a read-only head.

Such a sensor could be linked to control circuitry that monitors a conventional magnetic read head, so that the sensing means only became activated when tape carrying a magnetic signal was passing over the magnetic transducer.

This would allow the processor means to sense when the magnetisation of the tape drops below an expected level, indicating that a gap is opening up between the magnetic transducer and the tape.

Another way of detecting a gap is to use at least one electrical sensor for detecting the resistivity of the moving tape. Most tapes are designed with a moderate surface resistivity, for example through the choice of appropriate binders or surface coatings, in order to prevent the build up of static electricity on the surface of the tape as this is moving through the tape path. An electrical sensor can therefore be used to pass a very small current through the tape in order to detect its resistivity. In the case of a magnetic tape, this current can be made sufficiently small so that the current does not magnetise the tape. If a gap begins to open up between the measurement portion and the tape, the detected resistivity will begin to rise. The processor means can then take appropriate action.

A third way to measure a gap is to use at least one optical sensor for detecting the passage of light through a gap between the contact surface and tape moving across the contact surface. In this context, the term "light" means both visible and invisible light, including for example infrared light. Light can then be incident on the tape through a transparent or translucent window in the contact surface. As long as the tape remains in contact with the window, very little light will be transmitted or leak out from this area. If a gap begins to open up however, then more light will escape from the illuminated area. An optical sensor in the vicinity of the measurement portion can then detect this increase in light indicating the presence of the gap. Again, the processor means can halt the movement of the tape before the tape becomes seriously damaged.

The shape of the contact surface in the tape path can bearranged so that the gap to be detected is a separation of the tape and contact surface in the longitudinal direction. For example, a contact surface may have a curve in the longitudinal direction so that if the tape begins to lift away from the contact surface, a gap opens up above the contact surface progressively along the longitudinal direction.

Alternatively, a gap to be detected may be a separation of the tape and contact surface in the transverse direction.

In this case, the shape of the contact surface may be such that the gap opens progressively in the transverse direction, for example, moving from the edges to the centre as the tape tension becomes slackened.

In order to minimise wear between the tape and the contact surface, it is preferred if the contact surface is smoothly curving. The contact surface may, for example, be made from highly polished and plated metal which will not become abraded over time through contact with the moving tape.

The convex shape may have a circular cross-section, but in a preferred embodiment of the invention, the shape is parabolic or elliptical. This provides the advantage that when a gap starts to open up, the longitudinal or transverse direction over which the gap opens will be progressively greater as the rate of change of the curve lessens away from an apex of the parabola or ellipse. The apex may then be arranged in the median portion where it is expected that tape contact will not be lost.

Also according to the invention there is provided a method of detecting deviation of tape path in a tape transport mechanism, when the tape transport mechanism includes a device for detecting deviation of tape path according to the invention, the method comprising the steps of: a) loading the tape into the tape path b) moving the tape under tension along the tape path from the supply reel to the take up reel; c) using the tape contact sensor and processor means to verify contact of the tape with the contact surface; d) continuing to move the tape if tape contact is verified or stopping the tape if tape contact is not verified.

Preferably, the arrangement is such that the contact surface protrudes into the tape path upstream of the pinch roller arrangement so that when the tape is under tension, the tape naturally remains in contact with the median and measurement portions of the contact surface. The contact in the measurement region will then be affected to produce a gap between the tape and contact surface when the position of the tape path deviates.

The tape contact sensor may therefore be moveable between a rest position in which the tape is not in contact with the contact surface when the tape is in a correct tape path to a measurement position in which the tape is in contact with the contact surface when the tape is in the correct tape path. Then, the method may comprise additional after step a) and before c) the step of: e) moving the tape contact sensor from the rest position to the measurement position.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figures 1,2 and 3 show a conventional compact audio cassette and part of a tape drive mechanism, and stages involved in the wrapping of audio tape around a capstan roller; Figures 4 and 5 show in detail how the audio tape starts to wrap around the capstan roller; Figure 6 shows a plan view of a device for detecting deviation in tape path according to a first embodiment of the invention; Figure 7 shows a side view of the device of Figure 6; Figure 8 shows a plan view of the device of Figures 6 and 7 when the tape path deviates; Figure 9 shows a side view of a device for detecting deviation in tape path according to a second embodiment of the invention, together with a processor means and tape drive control means; Figure 10 shows schematically a device for detecting deviation in tape path according to a third embodiment of the invention; and Figure 11 shows the device of Figure 10 when tape path has begun to deviate.

Figure 1 shows a conventional compact audio cassette 1 having a supply reel 2, a take up reel 4, and idler rollers 5,6 and posts 7,8. The reels 2,4, rollers 5,6, and posts 7,8 are housed within a plastic housing 10, which has an opening 11 into which a magnetic read/write head 12 may be inserted in order to record or playback to tape 14 running along a tape transport path between the supply reel 2 and take up reel 4.

When the cassette 1 is loaded into a player, a capstan spindle 15 is inserted through an aperture 17 in the housing 10. An idler roller 20 is then brought to bear on the tape 14 and the capstan 15 upstream of the read/write head 12. The idler roller 20 and capstan spindle 15 form a pinch roller arrangement. Motors (not shown) then drive the capstan roller 15, as well as the supply and take up reels 2,4 in order to move the tape 14 along the tape path. Electrical power (not shown) for the motors and other electronics may be provided from a battery source or from rectified mains power.

If the tape becomes tacky or damaged, it may begin to adhere to the capstan spindle 15. When this happens, as shown in figure 2, the upstream tape will begin to be pulled around the rotating capstan spindle 15. Tape may also be puled around the capstan spindle 15 if tape tension is lost upstream of the pinch roller arrangement 15,20. If the tape is pulled as far as one revolution, then it can become trapped under tape leading to the capstan spindle 15, with the result that the tape rapidly begins to wrap itself around capstan spindle 15. Often, however, the tape will snap back off the capstan spindle 15, as shown in Figure 3. This results in a momentary loss of tension at a point 22 upstream of the capstan spindle 15.

Figures 4 and 5 show in greater detail how the path of the tape 14 begins to deviate in the region of point 22 when the tape beings to wrap around capstan spindle 15.

Figure 6 shows a first embodiment of a device 30 for detecting deviation of tape path in a tape transport mechanism. The device 30 is arranged so that when the read/write head 12 and idler roller 20 are brought to bear 31 against the tape, the device 30 is also moved 32 to protrude against the tape 14.

The device 30 has a very smooth and polished curved convex surface 34 which protrudes against the tape 14 when the tape is in motion along the tape path. The contact surface 34 has one portion 36 which is expected always to remain in contact with the tape 14 when the device 30 is moved to contact the tape 14. This portion 36 is referred to herein as a'median"portion. Downstream from the median portion 36 is another area 38 which it is expected might lose contact with the tape if the tape path deviates owing to the tape 14 beginning to wrap around capstan 15. This area 38 is referred to herein as a"measurement"portion.

Figure 7 shows areas 36 and 38 with different shading across the contact surface 34.

In the measurement portion 38 are two electrical contacts 40,41 spaced transversely either side of a centre line 42 of an expected tape path 43. When the tape 14 is running over the contact surface 34, a very small electrical current 44 is provided from electrical contacts 40,41 through the surface of the tape 14 in contact with the measurement portion 38. In this embodiment, the contact surface34 is formed from or coated in a non-conducting material, so that all of current 44 is through the tape 14. The device 30 has an output 44 to a microprocessor 46 in order to provide a signal to the microprocessor 46 representative of the level of the current 44 between the contacts 40,41. The microprocessor 46 then provides an output 48 to tape drive electronics 50. If the microprocessor output 48 indicates that tape contact is lost in the measurement portion 38, as shown in Figure 8 owing to a gap 52 between the contact surface 34 and tape 14, then the tape drive electronics 50 will stop the tape motion.

Figure 9 shows the second embodiment 60 of a device for detecting deviation of tape path. The device 60 has two magnetic read heads 62, 63 arranged in a measurement portion 38. Each magnetic read head 62,63 is along the centre line 42 of the expected tape path 43, with the magnetic heads 62,63 being spaced longitudinally, so that one magnetic head 63 is closest the median portion 36 of the contact area 34.

Each magnetic head 62,63 provides an output 65,66 to a microprocessor 68. If a magnetic signal is present at magnetic head 63, then the microprocessor 68 is programmed to expect a similar magnetic signal also at magnetic head 62. If the signal at the downstream magnetic head 62 drops below a predetermined level, then the microprocessor 68 interprets this as a gap between the contact surface 34 and the downstream magnetic head 62. The microprocessor then sends a control signal along an output line 70 to the tape drive electronics 50 in order to halt the motion of the tape 14.

Figures 10 and 11 show a third embodiment of a device 80 for detecting deviation of tape path. The device 80 has a curved convex contact surface 82 similar to that 34 for the first and second embodiments of the device 30,60. The device 80 however has two optical windows 84,85 in the measurement portion of the contact surface 82. The windows 84,85 are centred on the tape path, with one window 84 being longitudinally upstream the other window 85. The device 80 contains an optical source and detector pair 86 with an infrared source 87 separated from a matched infrared detector 88 by a surrounding housing 89. Infrared optical radiation 90 is incident through the upstream window 84 on the tape 14, and when the tape 14 covers the window 84, essentially no optical radiation 90 can find its way to the detector 88.

If the tape path begins to deviate, as shown in Figure 11, then some stray optical radiation 92 will find its way by scattering or multiple reflections into a gap 94 between the tape 14 and contact surface 82. Some of this stray radiation 92 will then be incident on the detector 88, with the result that the gap 94 can be detected. In order to improve sensitivity of the arrangement, the optical source 87 may be pulsed 96 so that a similar pulsed signal 98 may be received from the detector 88.

The detected signal 98 can then be passed to a microprocessor used to control tape drive electronics in a similar manner to that described above.

The invention therefore provides several ways in which deviation of tape path can be readily detected upstream of a pinch roller arrangement by detecting a gap owing to deviation of the tape path. Once such deviation is detected, action can be taken by control electronics to stop tape movement before the tape becomes wound around a roller.

Claims

Claims 1. A device for detecting deviation of tape path in a tape transport mechanism, comprising a tape contact sensor with an external contact surface and sensing means for detecting a gap between the contact surface and tape moving in a longitudinal direction across the contact surface, a processor means, an output from the sensor that provides to the processor means at least one signal representative of a detected gap between the contact surface and the tape, the processor being responsive to changes in the output signal in order to deactivate a tape transport mechanism in the event of a detected gap, in which the contact surface has in the longitudinal direction a convex shape over which moving tape may slide, the convex shape including a median portion and longitudinally adjacent this a measurement portion, wherein the sensing means is capable of detecting separation between a moving tape and the measurement portion when moving tape remains in contact with the median portion.
2. A device as claimed in Claim 1, in which the contact surface has in a direction transverse to the longitudinal direction a flat or a convex shape.
3. A device as claimed in Claims 2, in which the gap to be detected is a separation of the tape and contact surface in the transverse direction.
4. A device as claimed in any preceding claim, in which the gap to be detected is a separation of the tape and contact surface in the longitudinal direction.
5. A device as claimed in any preceding claim, in which the sensing means has two transducers for detecting the same physical property of moving tape, one transducer being arranged to detect the physical property in the median portion, and the other transducer being arranged to detect the physical property in the measurement portion, the at least one output signal being representative of the the detected property in the median and measurement portions.
6. A device as claimed in any preceding claim, in which the sensing means includes at least one magnetic transducer for detecting the magnetisation of moving tape.
7. A device as claimed in any of Claims 1 to 5, in which the sensing means includes at least one electrical sensor for detecting the resistivity of moving tape.
8. A device as claimed in any of Claims 1 to 5, in which the sensing means includes at least one optical sensor for detecting the passage of light through a gap between the contact surface and tape moving across the contact surface.
9. A device as claimed in any preceding claim, in which the convex shape of the contact surface is smoothly curving.
10. A device as claimed in Claim 9, in which the smoothly curving shape is parabolic or elliptical.
11. A tape transport mechanism loaded with a tape, comprising tape supply reel, a tape take-up reel, means to move the tape under tension along a tape path from the supply reel to the take-up reel, and a pinch roller arrangement in the tape path to control the tape movement, wherein the mechanism includes upstream of the pinch roller arrangement a device for detecting deviation of tape path as claimed in any preceding claim.
12. A tape transport mechanism as claimed in Claim 11, in which the contact surface protrudes into the tape path upstream of the pinch roller arrangement so that when the tape is correctly position in the tape path, the tape naturally remains in contact with the median and measurement portions of the contact surface, the contact in the measurement region being affected to produce a gap between the tape and contact surface when the tape path deviates.
13. A method of detecting deviation of tape path in a tape transport mechanism, the tape transport mechanism being as claimed in Claim 11 or Claim 12, the method comprising the steps of: a) loading the tape into the tape path b) moving the tape under tension along the tape path from the supply reel to the take up reel; c) using the tape contact sensor and processor means to verify contact of the tape with the contact surface; d) continuing to move the tape if tape contact is verified or stopping the tape if tape contact is not verified.
14. A method as claimed in Claim 13 when appendant from Claim 12, in which the tape contact sensor is movable between a rest position in which the tape is not in contact with the contact surface when the tape is in a correct tape path to a measurement position in which the tape is in contact with the contact surface when the tape is in the correct tape path, the method comprising additionally after step a) and before step c) the step of: e) moving the tape contact sensor from the rest position to the measurement position.
15. A device for detecting deviation of tape path in a tape transport mechanism substantially as herein described, with reference to or as shown in Figures 6 to 11 of the accompanying drawings.
16. A tape transport mechanism loaded with a tape substantially as herein described, with reference to or as shown in Figures 6 to 11 of the accompanying drawings.
17. A method of detecting deviation of tape path in a tape transport mechanism substantially as herein described, with reference to Figures 6 to 11 of the accompanying drawings.