WO2015028952A1

WO2015028952A1 - Fixed spool fishing reel

Info

Publication number: WO2015028952A1
Application number: PCT/IB2014/064094
Authority: WO
Inventors: Kevin Nash; John Hawker; Trevor Lloyd
Original assignee: Catchum 88 Limited
Priority date: 2013-08-28
Filing date: 2014-08-27
Publication date: 2015-03-05
Also published as: GB2517711A; GB201315310D0

Abstract

A fixed spool reel for a fishing line is disclosed that incorporates an apparatus (50, 54) for estimating the length of line unwound from the spool. The apparatus comprises a narrow detection light path defined by a light source (60) and a light sensor (64) mounted on the spool (10), the light path extending over the axial length of the spool and being interrupted by the fishing line as each turn of the line is unwound from the spool. A signal processing circuit (70) is connected to the light sensor (64) to detect and count interruptions of the detection light path. In the invention, a collimator (80, 82, 84) is provided to restrict the angular sensitivity of the sensor (64) to light that has travelled along the associated detection light path.

Description

Fixed Spool Fishing Reel

Field of the invention The present invention relates to a fixed spool fishing reel .

Background of the invention When fishing, an angler may wish to cast out the baited line to a specific region where fish are known to gather and feed. To assist the angler during casting to judge when the bait is at the specific region in the water, it is desirable to provide the angler with some indication of the length of line that has been unwound from the reel.

In one form of fishing reel, the drum about which the fishing line is wound is arranged with its axis

perpendicular to the length of the rod and the direction of line movement. As line is drawn from the reel, the drum rotates and it is possible to measure the length of line unwound from the drum by counting the number of times that the drum rotates. Such a reel however applies a severe drag that limits the distance to which the line can be cast out.

The type of fishing reel to which the present invention relates is known as a fixed spool fishing reel. In a fixed spool fishing reel, the axis of the spool about which the line is wound is disposed parallel to the length of the fishing rod. As its name implies, the spool may remain still when line is drawn from it, the line being simply unwound from the spool as it passes over and around the forward facing axial end plate of the spool. To wind the line back onto the spool, a bail arm is used to guide the line over the axial end face of the spool and to align its end

radially with respect to the spool axis. The bail arm is then rotated about the spool while the bail arm and the spool are moved axially relative to one another, to wind the line into a helical coil around the spool.

As fixed spool fishing reels are well known and are well documented in the prior art, it is not believed

necessary to describe them in greater detail. One of many examples of a fixed spool reel may be found in US 4,927,094 but it is stressed that the present invention is applicable to any fixed spool reel and is not restricted to any

particular design.

While fixed spool fishing reels have the advantage of being well suited to casting out light fishing lines they have hitherto suffered from the disadvantage that it has been difficult to determine the length of the line drawn from the spool during casting.

US 5,524,831, which is believed to represent the closest prior art to the present invention, describes a fixed spool reel for a fishing line incorporating an

apparatus for estimating the length of line unwound from the spool, the apparatus comprising a light source and a light sensor mounted on the spool. As it is unwound, the fishing line at one point round the circumference of the spool reflects light from the source back onto the sensor to allow the number of turns to be counted. In one contemplated embodiment, instead of reflecting light onto the sensor, the line interrupts a light path between the light source and the sensor.

Despite this prior proposal, no fixed spool reel has been successfully marketed that includes a turns counter. The reason for this is believed to reside in the inability of earlier proposed systems to operate reliably under a wide range of lighting conditions. Summary of the invention

According to the present invention, there is provided a fixed spool reel for a fishing line incorporating an apparatus for estimating the length of line unwound from the spool, wherein the apparatus comprises a narrow detection light path defined by a light source and a light sensor mounted on the spool, the light path extending over the axial length of the spool and being interrupted by the fishing line as each turn of the line is unwound from the spool and a signal processing circuit being connected to the light sensor to detect and count interruptions of the detection light path, characterised in that a collimator is provided to restrict the angular sensitivity of the sensor to light that has travelled along the associated detection light path.

In the present context, a collimator is to be taken to mean any device that reduces the spatial cross section of the beam of waves received by the sensor so that the sensor is shielded from light emanating from sources other than the light source mounted on the spool. In embodiments of the invention, the collimator may be embodied as a hood

comprising a baffle spaced from the light sensor or a plurality of baffles spaced from on another, each baffle having a hole lying in the light path leading to the sensor.

The term "light" as used herein is intended to include both visible light and radiation, such as infra-red and ultraviolet, that falls outside the range visible to the human eye.

When line is drawn axially from a fixed spool, the point of contact of the line with the perimeter of the forward facing axial end face of the spool rotates through 360° for each turn that is unwound from the spool. If therefore a light path is defined that is fixed relative to the axial end faces of the spool, that light path will be interrupted each time that it is crossed by the line and each interruption will therefore indicate that one turn has been unwound from the spool. By sensing the interruptions of a light path by the turns of line unwound from a fixed spool reel, it is possible for the total length of line drawn from the reel during casting to be estimated.

The present invention in its mina aspect minimises interference from extraneous light sources, and in

particular the sun, by providing a hood to shield each sensor so that its angular range of sensitivity is

restricted to light that has travelled along the associated detection light path, the hood comprising a baffle spaced from the light sensor or a plurality of baffles spaced from on another, each baffle having a pin hole lying in the light path leading to the sensor.

The diameter of the pin hole should preferably be no greater that three times the diameter of the fishing line and should, more preferably, be equal to or less than the diameter of the fishing line.

Detection of interruption of a detection light path has not hitherto proved to be sufficiently reliable and is prone to both false positive and false negative detection of light path interruptions. False positive can be caused, for example by flickering of the light source or something in the air, such as dust or rain, while false negatives can be the result of the sensor being blinded by a bright light, such as the sun, and not being able to sense the slight reduction in light intensity cause by the interruption of the detection light path. This is especially problematic when using a line of small diameter.

In an alternative aspect of the invention, reliability of detection is improved by providing two or more detection light paths, whereby two or more interruptions of a

detection light path are sensed by the signal processing circuit as each turn is unwound from the spool. In

embodiments having multiple detections paths, the

reliability of detection may be sufficiently improved to render superfluous the need to shield the sensor from extraneous light by using a hood.

In some embodiments, the signal processing circuit is operative to correlate the signals indicative of

interruption of the difference detection light paths, the turns count being incremented or decremented only in

response to sensing of successive interruptions in two detection light paths.

It is possible to provide two detection light paths using only a single light source and a single sensor mounted on the same axial end of the spool if a reflector is mounted on the opposite axial end of the spool to reflect light emitted by the light source to the light sensor. The

reflector in this case may comprise two reflecting surfaces spaced apart by the same distance as the light source and the reflector whereby the two detection light paths lie parallel to one another. By using a 90° prism as a double reflector instead of mirrors, and relying on total internal reflection within the prism, one can avoid the problems that occur when using silvered surfaces in hostile environments.

In an arrangement using a folded light path and only one light sensor, it is not possible to determine which order the two halves of the light path are interrupted and the sensor output alone is not therefore indicative of whether line is being played out from the reel or wound back onto the reel. Instead, one may use of a switch operated by the bail arm of the reel to indicate when line is being wound back onto the reel. In alternative embodiments, two light sensors may be arranged at one axial end of the spool and one or more light sources arranged on the opposite axial end of the spool. In this case, signal processing circuit connected to the light sensors may be operative to count up when a first of the detection light paths is sensed to be interrupted before a second and to count down then the first of the detection light paths is sensed to be interrupted after the second. Interference from other light sources may also be reduced by placing an optical filter in the light path leading to each sensor to allow light of the wavelength emitted by the associated source to pass while attenuating light of other wavelengths.

The signal processing circuit may include an analogue circuit to amplify the sensor output and detect

interruptions of the associated detection light path as well as a digital circuit programmed to perform digital filtering of the pulses received from the analogue circuit to

discriminate against false positive indications of

interruptions of the detection light paths.

The digital processor may serve to compare the time intervals between consecutive detected line interruptions in order to compensate for false negative indications of light path interruptions. By relying on both auto-correlation of the output signal of each sensor and cross-correlation of the output signals of different sensors the signal

processing circuit can discriminate against both false positive and false negative detections.

For example, upper and lower limits may be placed by an algorithm on the duration of a pulse that can be taken to be indicative of a light path interruption. This is based on the fact that within the range of speeds at which line can be drawn from a reel during casting, there is only a limited range of times that the line can interrupt the light path between the source and the sensor.

In a similar way, one can place a lower limit on the time between pulses.

If a system of mirrors is used to create a folded light path, auto-correlation of the output signal of the sensor will eliminate false alarm by detecting only interruptions where the light path is interrupted twice within a given time window.

Though referred to as a "fixed spool" reel, it is common for the reel to be rotatably supported on an axle that is secured to the fishing rod and for a device to be provided to vary the amount of frictional resistance, or drag, encountered by the spool as it rotates.

In such a construction, it is important for both the light source and the light sensor to be mounted for rotation with the spool. Conveniently, the light source, the light sensor and any mirrors are mounted on the axial end plates of the spool and the circuitry for powering the light source and analysing the output signal of the sensor may be mounted within the spool between a cylindrical surface about which the line is wound and the fixed axle about which the spool rotates .

Input and output devices, such as setting buttons and a counter display, may be mounted on axial end faces of the spool. Alternatively, such input and output devices may be mounted in a separate housing that communicates with the spool mounted circuitry, for example by radio or through slip rings.

As the line is cast, the angler will be following the end of the line visually and therefore unable to watch the count displayed on a counter at the same time. It is therefore preferred for the apparatus to include a sound generator for producing audible signal to assist the angler in determining when the desired length of line has been drawn from the reel. For example, the apparatus may emit a series of beeps that increase in frequency as line is drawn from the spool and become continuous when the desired range has been reached. If desired, the beeps may cease to be continuous if the line overshoots the desired range.

In the event of an overshoot, the angler can wind line back onto the spool using the bail arm. The apparatus is advantageously switched to count in the opposite sense when line is pulled back and the length of line that is rewound on the spool may be determined either by counting rotation of the bail arm or by counting interruptions of the light path by the line.

It is currently common for anglers to use two fishing rods, one having only a weight and a float and the other for the baited line. The first rod is used only to determine the depth of the water and to leave a float as a marker to assist in casting the line of the second rod. With the aid of the present invention, it is possible to use the same rod both to identify a suitable region in the water and to cast a line out reliably to that region without the need for a visible marker. First a weight and a float are attached to the line and it is cast to find a suitable location in the water. Once the desired location has been found, a button may be pressed to memorise the count indicative of the length of line that has been drawn from the spool and that count may be used during the subsequent casting of the baited line to ensure that the bait has reached the desired location .

While the apparatus as described so far is capable of providing range information to assist the angler to cast out to a desired distance it does not provide any azimuth information. This often does not present problem as the angler may be able to use features or landmarks on the opposite bank to determine the direction of casting. It is nevertheless possible to provide azimuth information, if required, by incorporating a compass into the same or a separate apparatus and displaying the bearing of the desired location during casting. The "compass" need not be a rotating magnet but may be a MEMS (Micro-Electro-Mechanical Sensor) device sensitive to the earth's magnetic field.

Absolute calibration of the range and azimuth signals is of course not necessary as the aim of the apparatus is only to return to the same location each time.

It is also possible to use a MEMS sensor to determine the inclination of the fishing rod and to use that

information to determine whether line is being drawn from the spool or being wound back onto the spool. The rapid change in inclination of the rod may be used to reset the turns counter and to start counting upwards. After return of the rod to a generally horizontal position, all further detected interruptions of the detection light path may be used to reduce the count as the line can then only be wound back onto the reel.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawing, in which :

Figure is a schematic section through the spool of a reel embodying the first aspect of the invention, Figure 2 is a schematic representation of a folded light path of the embodiment of the invention shown in

Figure 1,

Figure 3 is schematic block diagram of a circuit for counting the number of turn unwound from a fixed spool fishing reel, and

Figure 4 is a schematic block diagram similar to that of Figure 3 of an embodiment in accordance with the second aspect of the invention for indicating when the fishing rod is pointing in the desired azimuth direction.

Detailed description of the embodiment ( s )

Figure 1 is a schematic detail of a fixed spool fishing reel showing a spool 10 about which fishing line is wound and an axle 12 rotatably supporting the spool, the axle being fixed relative to a housing (not shown) that is secured to the fishing rod. Though the spool 10 is described as being fixed (because it does not need to rotate for line to be drawn from it) , it is capable of rotating relative to the axle 12. At its axial front end, shown on the right in the drawing, a hand wheel 14 is screwed onto the axle 12 and acts on a friction washer 16 through a spring 18 to control the drag experienced as the spool 10 rotates about the axle, the axle being clamped axially between the friction plate 16 and a stop 20 on the axle, which may be a machined shoulder or a transversely inserted pin.

There are other forms of reel in which the axle is fixed to the spool, the axle being rotatably supported in the housing secured to the fishing rod. In such a

construction, the mechanism for controlling the drag on the spool may be mounted on the opposite end of the axle. A bail arm assembly (not shown) for winding the fishing line back onto the spool 10 is rotatable about the axle 12 and is coupled by means of a gearbox to a manually operated crank arm extending at right angles to the fishing rod. The gearbox includes bevel gears and is disposed within the housing of the fishing reel that is secured to the fishing rod .

All the parts described above are conventional and will be well understood by the person skilled in the art without the need for further explanation. A typical gearbox and a bail arm assembly are described in US 4,927,094.

The present invention is not concerned with the

operation of the fishing reel but, in its first aspect, is concerned with an apparatus that is mounted on the spool to measure the number of turns of line unwound from the spool. The apparatus relies on the fact that if a light path is defined between the two axial ends of the spool at any point around its circumference, line pulled axially off the end face of the spool will interrupt that light path once for each turn that is unwound from the spool. By counting the number of interruptions of the light path, it is therefore possible to provide a reading indicative of the total length of line that has been drawn from the spool.

In the embodiment of the invention shown in Figure 1, the apparatus comprises a ring 50 that is secured to the perimeter of the forward facing axial end plate 52 of the spool 10, and an annular body 54 that fits within the opposite end of the spool 10. The annular body 54 has an axial end flange 56 of greater diameter than the rearward facing axial end plate 58 of the spool 10, such that parts of both the ring 50 and the flange 56 project radially beyond the axial end plates of the spool 10. Within the radially projecting region of the flange 56 there are mounted a light source 60 and a light sensor 64. The light sensor 64 is not present in the section of Figure 1 but is shown in Figure 2. Within the radially projecting region of the ring 50, there is mounted a

reflector 62, which as shown in Figure 2 may comprise two prisms 62a and 62b. The light source 60, the reflector 62 and sensor 64 are all recessed deeply within the ring 50 or the flange 56, so as to be shielded from extraneous light.

In operation, light emitted by the source 60 travels to the reflector 62 and then returns to the sensor 64 thereby defining two light paths that extend from one axial end of the spool 10 to the other. If, as shown in Figure 2, the reflector 62 comprise two reflecting surfaces spaced apart by a distance equal to that between the light source 60 and the light sensor 64 on the flange 56, then the two paths extend parallel to one another and are tangentially offset from one another.

The annular body 54 carries an electronic circuit 70, cells 72 for powering the circuit 70, and I/O (input/output) devices 74 communicating with the circuit 70. The I/O devices may include buttons, LED's and an LCD display. They may also include a sound generator or a radio transmitter.

The circuitry for determining the number of turns unwound from the spool need not be mounted on the spool, as illustrated in Figure 1, if there is insufficient available space. The only components that need to be mounted on the spool are those defining the detection light path that is interrupted by the line as turns are unwound from the spool. The output signal from the sensor 64 and the power supply to the light source 60 may for example pass through slip rings on the axle 12.

Figure 2 shows an arrangement that reduces interference from extraneous light sources. The light source 60 and the sensor 64 are fitted with hoods 80, 82 that are painted matt black on their interior and may have a series of baffles to minimize light bouncing off the inner walls of the hoods. The light source may be fitted with a collimator lens 84 to maximise the intensity of the light directed towards the sensor 64 and the latter may be fitted with a filter 86 to let through only light of the wavelength emitted by the light source 60.

To improve the signal to noise ratio further, it has further been found advantageous to provide in the light path leading to the sensor 64 a pin hole aperture of a diameter no greater than that of the line.

Referring now to Figure 3, the output signal of the sensor 64 is applied to a pulse detector 90. The latter is an analogue circuit that first amplifies the output signal from the sensor 64 then compares the amplified signal with a reference threshold to sense interruptions of the light path by the fishing line.

The output signals of the pulse detector is applied to a digital processor 94 which, in the same manner as other microcomputers, communicates with a read only memory (ROM) 96, a random access memory (RAM) 98 and a clock circuit 100. The processor 94 operates under control of a program stored in the ROM 96 to perform digital filtering on the signals received from the pulse detector 90 and its input/output (I/O) circuits includes set/reset buttons 92, an LCD display 102 and a sound generator 104.

The purpose of the digital filtering is to ensure accurate pulse counting by discounting false positives and compensating for false negatives in the signal from the pulse detector.

As the circuit is intended to assist with casting, when the line is moving quite rapidly, the output of the pulse detector should comprise pulses having a duration and a repetition frequency lying within limited ranges. Furthermore, when the light path is folded (as shown in Figure 2), and within each signal cycle, corresponding to one turn of line being withdrawn from the coil, there should be two closely spaced pulses separated in time by a period dependent on the cycle repetition frequency. If the two legs of the light path are parallel to one another, as shown in Figure 2, then the time duration between the pulses will not vary with the axial position along the spool from which the line is drawn.

The digital filtering can thus be used to reject pulses of which the duration and the repetition frequency lie outside permitted time windows. By auto-correlation, the processor can also reject pulses that do not appear as one of a pair. Such filtering may therefore reliably

discriminate against false positives. Also, because during casting, a line cannot stop in mid-air and then resume its previously measure speed, when a measured cycle has a duration that approximate to twice the average of the preceding and following cycles, it may be assumed that a false negative has occurred.

When the processor has evaluated that a turn of line has been drawn from the fixed reel, it increments a counter the output of which is shown on the display 102. The sound generator 104 at the same time may issue beeps, the

frequency of which increases as the total length of line drawn from the spool approaches the desired distance to which the bait is to be cast.

It is possible to use the same method both when casting and when using the bail arm to wind line back into the spool. The direction of counting may be reversed by the angler pressing a button before winding line back onto the spool or by a switch operated when the bail arm is moved into the position for winding the line back onto the spool. It is further possible to detect the direction or rotation automatically, using two asymmetrically located light sensors. In such a case, on account of the duplication of the light sensors, correlation of their output signals can also assist in improving the reliability of line detection.

In operation, an angler may first cast out using the fishing rod with only a weight and a float to find a

position in the water where fish are likely to be feeding. The weight and the float can be used in the usual way to determine if the depth of the water is appropriate. Having now determined the compass bearing of the desired position, either by alignment with a landmark on the opposite bank or by taking a compass bearing, the angler resets the counter to zero and winds the line back onto the reel.

As it is being rewound, the number of turns of line can be determined either by counting the rotations of the bail arm or by counting the interruptions of the light path of the apparatus of the invention by the fishing line. The number of turns may not be linearly related to the length of line as the spool diameter will change but that is not of importance as the angler need not know the exact length of line, just as long as he can cast out again to the same position .

After the line has been wound back onto the spool, the angler can attach the line the rig and the bait that he wishes to use and cast out again in the desired direction. As line is drawn from the spool, the counter will now count in reverse and the displayed count will be decremented. At the same time, the sound generator 10 will produce beeps of which the frequency increases as the length of line drawn from the spool approaches the desired length and as the displayed count diminishes towards zero. When very near the desires position in the water, the sound generator produces a continuous tone. At this time, the angler using a finger over which the line is passed during casting, will trap the line against the fishing rod to prevent any more line from been pulled off the spool.

As the angler cannot move the angling rig further out if the line has not been cast out sufficiently, the angler will tend to overshoot the desired region in the water.

This will be indicated by the continuous tone emitted by the sound generator 104 reverting to fast beeps. The angler can then rewind line back onto the spool using the bailing arm until the counter reading is again zero and a continuous tone is produced by the sound generator 104. It has been mentioned above that the correct direction in which the line is to be cast may be determined using a compass. It is known that compass bearings may be obtained from small MEMS sensors as are to be found, for example, in certain "smart phones". Such a sensor may be built into an apparatus using the same or similar circuitry to that described above.

A circuit of an apparatus, in accordance with the second aspect of the invention, for indicating that the rod is pointing in the desired direction is shown in Figure 4. The circuit of Figure 4 differs from that of Figure 3 only in that the pulse detector is replaced by a magnetic sensor.

In Figure 4, the output of the magnetic MEMS sensor 150 is be applied to a processor 152 connected to a ROM 154, a RAM 156, a clock 158 and having as I/O devices set/reset buttons 160, a digital display 162 and a sound generator 164. After the line has been cast to the desired region, a button 160 is pressed by the angler to cause the output of the MEMS sensor 160 to the stored in RAM 156. Subsequently, during casting, the display 162 and the sound generator 164 serve the indicate to the angler the difference between the prevailing compass bearing and the desired bearing in the same way as described above for indicating the difference between the length of line drawn from the spool and the desired length.

In view of the similarity between the circuits of Figures 3 and 4, it will be clear the same circuitry may be used to embody both aspects of the invention. Hence, the same processor 94 may be connected both to a pulse detector 90 and a MEMS sensor 150 and one of the control buttons 92 may be serve a mode selection button to choose between compass bearing and distance.

It is of course alternatively possible to use a first apparatus to determine the correct range and separate apparatus to determine the correct azimuth.

It will be clear to the person skilled in the art that various modifications may be made to the preferred

embodiment of the invention described above within the scope of the appended claims.

For example, the embodiment shown in Figures 1 and 2 avoids the need for wires connected to both axial ends of the spool but it is alternatively possible to mount the light source 60 and the light sensor 64 on opposite axial ends of the spool 10.

Furthermore, while the entire circuitry has been shown as mounted on the spool, it is alternatively possible to mount only selected components of the circuitry on the spool and provide the remaining components in a stationary

separate housing that communicates with the spool either through slip rings or through non-contact coupling, such as by inductive coupling or by radio transmission. If desired, one may provide an RF or Bluetooth link in the reel unit which can be used for sending data for a handset to collect. This would allow the user to

upload/download casting information. This would also allow for GPS coordinates to be logged.

It is further possible for the beeps during line pay^¬ out to change tone to indicate that the line is approaching its desired destination.

Claims

1. A fixed spool reel for a fishing line

incorporating an apparatus for estimating the length of line unwound from the spool, wherein the apparatus comprises a narrow detection light path defined by a light source and a light sensor mounted on the spool, the light path extending over the axial length of the spool and being interrupted by the fishing line as each turn of the line is unwound from the spool and a signal processing circuit being connected to the light sensor to detect and count interruptions of the detection light path, characterised in that a collimator is provided to restrict the angular sensitivity of the sensor to light that has travelled along the associated detection light path.

2. A fixed spool reel as claimed in claim 1, wherein the collimator is formed as a hood comprising a baffle spaced from the light sensor or a plurality of baffles spaced from on another, each baffle having a hole lying in the light path leading to the sensor.

3. A fixed spool reel as claimed in claim 2, wherein the hole is a pin hole having a diameter no greater than three times that of the fishing line, being, more

preferably, equal to or less than the diameter of the fishing line.

4. A fixed spool reel as claimed in any preceding claim, wherein two or more detection light paths are

provided, whereby two or more interruptions of a detection light path are sensed by the signal processing circuit as each turn is unwound from the spool.

5. A fixed spool reel as claimed in claim 4, wherein the signal processing circuit is operative to correlate the signals indicative of interruption of the different detection light paths in order to improve the reliability of detection of the passage of fishing line, the turns count being incremented or decremented only in response to sensing of successive interruptions in two detection light paths.

6. A fixed spool reel as claimed in claim 4 or 5, wherein a single light source and a single sensor are mounted on one axial end of the spool and a reflector is mounted on the opposite axial end of the spool to reflect light emitted by the light source to the light sensor so as to define two detection light paths.

7. A fixed spool reel as claimed in claim 6, wherein the reflector comprises two reflecting surfaces spaced apart by the same distance as the light source and the sensor whereby the two detection light paths lie parallel to one another .

8. A fixed spool reel as claimed in claim 7, wherein the reflector is a 90° prism.

9. A fixed spool reel as claimed in claim 4 or 5, comprising two light sensors arranged at one axial end of the spool and one or more light sources arranged on the opposite axial end of the spool.

10. A fixed spool reel as claimed in claim 9, wherein the circuit connected to the light sensors is operative to count up when a first of the detection light paths is sensed to be interrupted before a second and to count down then the first of the detection light paths is sensed to be

interrupted after the second.

11. A fixed spool reel as claimed in any preceding claim, wherein an optical filter is placed in the light path leading to each sensor to allow light of the wavelength emitted by the associated source to pass while attenuating light of other wavelengths.

12. A fixed spool reel as claimed in any preceding claim, wherein signal processing circuit includes an

analogue circuit to amplify and process the output signals of the sensor in order to detect brief interruptions of the associated detection light path.

13. A fixed spool reel as claimed in claim 12, wherein the signal processing circuit further includes a digital circuit programmed to perform digital filtering of the pulses received from the analogue circuit to discriminate against false positive indications of interruptions of the detection light paths.

14. A fixed spool reel as claimed in claim 12 or 13, wherein the digital processor is operative to compare the time intervals between consecutive detected line

interruptions in order to compensate for false negative indications of light path interruptions.

15. A fixed spool reel as claimed in any preceding claim, in which some of the components of the apparatus for counting the number of turns unwound from the spool are mounted on the spool while others are mounted in a separate stationary housing and communicate with the spool components by one or more slip rings or by a wireless connection.

16. A fixed spool reel as claimed in any of claims 1 to 14, in which all of the components of the apparatus for counting the number of turns unwound from the spool are mounted on the spool.