GB2423574A

GB2423574A - Optical tape sensor

Info

Publication number: GB2423574A
Application number: GB0503876A
Authority: GB
Inventors: Ian Gibb
Original assignee: Macon Management and Design Ltd
Current assignee: Macon Management and Design Ltd
Priority date: 2005-02-25
Filing date: 2005-02-25
Publication date: 2006-08-30
Also published as: GB0503876D0

Abstract

A bundler system in which a band of tape is placed around a plurality of objects, such as envelopes, pulled tight, welded and cut to hold the objects together, comprising a banding mechanism having a tape sensor. The tape sensor has an emitter 1 and two detectors 2 and 3 one arranged to receive radiation from the emitter transmitted through the tape 5 and the other arranged to receive radiation reflected from the tape 5. Signals from the detectors 2 and 3 are fed to signal processing electronics 8 operative to produce an output indicating the presence or absence of tape. This provides a non intrusive device which enables the position of different types of tape (e.g. clear plastic and paper) to be accurately determined facilitating the banding operation in a bundler system.

Description

A TAPE SENSOR

The present invention relates to a tape sensor.

There are a number of different applications in which the reliable sensing of a tape is of prime importance. One such is a mail bundling system in which envelopes are stacked in individual stacks and held together by tape in bands. A requirement is to be able to use different materials for banding tape, such as paper or plastic film and to accurately control the size of the banding ioop and the tension of the band when it is made.

There are many methods that have been used to detect the position of tape in various mechanisms. One common method is to use an optical approach that uses an emitter and detector positioned in either a reflective or diffused arrangement. This approach relies on the material being either reflective or non-transparent so that there is a measurable difference in the light detected at the sensor when the tape is present.

An alternative optical method is to use polarising filters on either side of the tape and detect the tape using the fact that the light is polarised as it passes through a transparent object. Mechanical methods have been used where the tape must move an actuator that, in turn, operates a micro switch or obscures an optical detector.

A disadvantage of these methods is that they do not perform satisfactorily with different types of tape. It is an object of the invention to mitigate these disadvantages.

According to the present invention there is provided a tape sensor comprising an emitter for emitting radiation, a first detector for detecting radiation emitted by the emitter, and a second detector for detecting radiation emitted by the emitter, the position of the first and second detectors in relation to the emitter being such that, in operation the first detector receives radiation from the emitter transmitted through the tape and the second detector receives radiation reflected from the tape and a signal processor connected to the detectors to receive signals therefrom and to produce from those signals an output indicating the presence or absence of tape.

According to another aspect of the present invention, there is provided a banding mechanism including a tape drive mechanism and a tape sensor comprising an emitter for emitting radiation, a first detector for detecting radiation emitted by the emitter, and a second detector for detecting radiation emitted by the emitter, the position of the first and second detectors in relation to the emitter being such that, in operation the first detector receives radiation from the emitter transmitted through the tape and the second detector receives radiation reflected from the tape and a signal processor connected to the detectors to receive signals therefrom and to produce from those signals an output indicating the presence or absence of tape.

According to a further aspect of the invention there is provided a bundler system comprising a banding mechanism including a tape drive mechanism and a tape sensor comprising an emitter for emitting radiation, a first detector for detecting radiation emitted by the emitter, and a second detector for detecting radiation emitted by the emitter, the position of the first and second detectors in relation to the emitter being such that, in operation the first detector receives radiation from the emitter transmitted through the tape and the second detector receives radiation reflected from the tape and a signal processor connected to the detectors to receive signals therefrom and to produce from those signals an output indicating the presence or absence of tape.

In a preferred embodiment of the invention, the emitter is a light emitting device, such as for example, a light emitting diode (LED) which may operate in the visible or infra sectors of the electromagnetic spectrum. In operation an AC supply is used to drive the LED at a frequency several octaves above the frequency at which fluorescent lights radiate to reduce the possibility of conflict with emissions from such sources. The detectors are advantageously positive intrinsic negative diodes (PIN) or phototransistors. The first detector is located in line with the optical axis of the emitter and the second detector is located on the same optical plane as the emitter, but at an angle to receive light from the emitter reflected by the tape. This angle may be varied to increase or maximise radiation received. The signal processor produces a difference value from the detector signals received which may be used to detect the presence or absence of tape. The processor may be calibrated to different types of tape. The calibration process determines two threshold values which are used to decide if the sensor is clear (tape absent) or blocked (tape present). The tape drive mechanism preferably comprises two pinch rollers through which tape may be fed. One roller is driven by a motor having a shaft encoder under the control of a motor drive circuit and associated control system, which, in use, is used to create a servocontrol loop operating a speed and position control system means for controlling position of the tape.

In order that the invention may be more clearly understood, one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 diagrammatically shows a tape sensor, according to the invention; Figure 2 is a block circuit relating to the electronic circuitry of the sensor of Figure 1 and the operation of associated computer software; Figure 3 shows a banding mechanism comprising a tape drive mechanism and the tape sensor of Figure 1, and Figure 4 diagrammatically shows a mail bundler system of which the sensor of Figures 1 to 3 forms part.

Referring to Figure 1, the tape sensor comprises an emitter 1, two detectors 2 and 3 and signal processing electronic and associated software 4. A tape to be sensed is shown at 5. The two detectors 2 and 3 are disposed on opposite sides respectively of the tape 5 so that, in operation, detector 2 receives radiation transmitted through the tape 5 from emitter 1 and detector 3 receives radiation reflected from the tape from emitter 1. The emitter 1 is a light emitting device such as a semiconductor light emitting diode (LED). The light emitted may be visible or infrared. To avoid conflict from ambient light sources such as fluorescent lights, an alternating current (AC) signal is used to drive the LED at a frequency several octaves above the frequency at which the fluorescent lights operate and radiate.

The detectors 2 and 3 are chosen to operate at substantially the same frequency as the emitter 1. The detectors may be positive intrinsic negative (PIN) diodes or phototransistors. Detector 2 is disposed in line with the optical axis of the emitter 1 and light radiation is transmitted along that line referenced 6 in Figure 1, from emitter 1 to the detector 2.

Detector 3 is disposed on the same optical plane as emitter 1 but positioned to receive light radiation emitted from emitter 1 along a line 7 by reflection from the tape 5. The position of detector 3 in relation to emitter 1 may be varied as desired in order to maximise the received reflected radiation. The angle between the normal to tape 5 and line 7 may vary but in this case is 700. The emitter 1 and detectors 2, 3 are symmetrically arranged in relation to tape 5 and so the angle between the normal and line 6 is also 70 . The angle chosen will vary depending upon the material or materials of the tape and its refractive index. The refractive index of the tape governs the angle at which total internal reflection occurs. For example, for polyethylene, the refractive index varies between 1.5 and 1.7 giving a range of 36 to 42 degrees from the normal for total internal reflection but different materials will produce different figures.

In operation, the detectors 2 and 3 produce signals which are fed to signal processing electronics indicated generally in Figure 1 at 8. this circuitry 8 is shown in more detail in Figure 2. Referring additionally to Figure 2, the detectors 2 and 3 are connected in series to respective AC coupled amplifiers 9 and 10, bandpass filters 11 and 1 2 and peak detectors 1 3 and 1 4. The outputs from peak detectors 1 3 and 1 4 are fed to an analogue to digital converter 1 5.

The signals output from detectors 2 (transmitted) and 3 (reflected) are amplified in respective AC coupled amplifiers 9 and 10. The outputs are then filtered in respective band pass filters 11 and 1 2 before passing into respective peak detectors that generate DC voltages proportional to the magnitude of the amplified AC peak signals. This method has several advantages for this application including eliminating effects of DC light, e.g.: incandescent and sunlight. The band pass filters eliminate low frequency AC signals such as emitted by fluorescent lights; and effects of DC offsets in the high-gain amplifier stages is minimised.

The outputs of the peak detectors are then fed into the analogue to digital converter 1 5 so that the remainder of the signal processing can be performed in software loaded onto the electronics.

The program takes a sample of the peak detector outputs at regular intervals and calculates the average of the signals from detector 2 and detector 3 at 16. A calculated result is taken from these average values where: Result = (average of detector 2) - (average of detector 3) at 1 7 This result is then compared with two reference threshold values that have previously been determined during a calibration procedure.

These thresholds are "Clear_Threshold" and "Blocked_Threshold" shown diagrammatically at 18 and 19. Using two thresholds provides hysteresis so that small perturbations of the peak detector outputs do not cause invalid decisions from the tape sensor. The output of the comparison with the two threshold values determines if the tape is, or is not, detected by the tape detector arrangement represented respectively by boxes 20 and 21. An additional box 22 indicates no change in detector.

The tape sensor arrangement may form part of a banding mechanism. Such a mechanism is illustrated diagrammatically in Figure 3.

Referring to Figure 3 the banding mechanism comprises a tape drive mechanism having a pair of pinch rollers 25 and 26 between which the tape 5 passes. One of the rollers 26 is driven by means of a DC motor 27 which has a shaft encoder 28. The direction of rotation of the motor 27 determines the direction of rotation of the pinch rollers 25 and 26 and thus the direction of movement of the tape 5 either forward towards the tape sensor (as indicated by arrow 29) or away from the tape sensor.

The motor 27 is controlled by a motor drive circuit and associated control system indicated generally at 30. This comprises the tape sensor signal processing electronics and software 8 already described and encoder signal processing electronics. The motor drive circuit and associated control system is used to create a servo-control loop which, in use, operates as a speed and position control system.

The banding mechanism may be used in a bundler system in which a band of tape is placed around a plurality of objects and the tape pulled tight, welded and cut to hold the objects together. Such an arrangement is described with additional reference to Figure 4 which diagrammatically illustrates a mail bundler system in which the objects to be banded are envelopes. The system comprises a collating station 33 and a bander 34.

Envelopes to be bundled are supplied to the mail bundler in the direction of arrow 35 passing first to the collating station where the envelopes are stacked to a predetermined height. The stacks are then fed successively to the bander 34. Generally more than one bander 34 will be provided.

To register the tape, Tape is supplied to the tape sensor (Figure 1) until the sensor is detected as being blocked. The motor 27 (Figure 3) is then stopped. The motor 27 is then restarted to generate a loop of tape in the bander of a predefined length having regard to the stack height of envelopes to be banded. The stack of objects are then placed inside the loop. Once banded the severed tape end is then registered again, using the motor control system and tape sensor so that the next loop of tape can be reliably generated ready for the next banding operation.

This arrangement gives the ability to reliably detect the presence of tape, whether opaque, transparent or translucent or combinations of these, e.g.: printing on otherwise transparent tape. In a banding mechanism it is advantageous to have accurate knowledge and control of the tape position as this improves the reliability and integrity of the banding mechanism. The tape sensor described above also has the advantage that it is non-intrusive to the banding mechanism in the vicinity of the tape and has the possibility of being made very small using modern semiconductor and circuit assembly techniques.

As well as detecting the position of the tape while it is being fed, the sensor can also be used to detect the tape in the correct position to confirm that a band has been successfully made.

Consistent position of the tape in the banding mechanism has the advantage of improving the reliability of the banding operation.

Other methods used previously to detect the tape position use a mechanical switch that the tape must displace. This method also tends to be bulky and must be placed directly in the tape path. They also require operating with a very light action if they are to be used with thin tapes.

Being able to detect the tape position or presence/absence during the banding cycle also allows for better error detection when the bander is incorporated in a larger system, such as the mail bundling system described.

It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention.

Claims

1. A tape sensor comprising an emitter for emitting radiation, a first detector for detecting radiation emitted by the emitter, and a second detector for detecting radiation emitted by the emitter, the position of the first and second detectors in relation to the emitter being such that, in operation the first detector receives radiation from the emitter transmitted through the tape and the second detector receives radiation reflected from the tape and a signal processor connected to the detectors to receive signals therefrom and to produce from those signals an output indicating the presence or absence of tape.

2. A tape sensor as claimed in claim 1, in which the emitter is a light emitting device.

3. A tape sensor as claimed in claim 2, in which the light emitting device is a light emitting diode.

4. A tape sensor as claimed in claim 3, in which the light emitting diode is adapted to operate in the visible light sector of the electromagnetic spectrum.

5. A tape sensor as claimed in claim 3, in which the light emitting diode is adapted to operate in the infra sector of the electromagnetic spectrum.

6. A tape sensor as claimed in any of claims 2 to 5, in which an AC supply is provided operative to drive the light emitting diode at a frequency different from the frequency at which ambient fluorescent lights operate to reduce the possibility of conflict with emissions from such lights.

7. A tape sensor as claimed in any preceding claim, in which the detectors are positive intrinsic negative (PIN) devices.

8. A tape sensor as claimed in claim 7, in which the positive intrinsic negative devices are diodes.

9. A tape sensor as claimed in claim 7, in which the positive intrinsic negative devices are phototransistors.

10. A tape sensor as claimed in any of claims 1 to 6, in which the detectors are phototransistors.

11. A tape sensor as claimed in any preceding claim, in which the first detector is located in line with the optical axis of the emitter and the second detector is located in the same optical plane as the emitter but at an angle to receive radiation from the emitter reflected from the tape.

12. A tape sensor as claimed in claim 11, in which in operation, the angle may be varied to increase radiation received by the second detector.

13. A tape sensor as claimed in any preceding claim, in which the signal processor produce a difference value from the detector signals received.

14. A tape sensor as claimed in any preceding claim, in which means are provided for calibrating the signal processor to different types of tapes.

1 5. A banding mechanism including a tape drive mechanism and a tape sensor as claimed in any preceding claim.

1 6. A banding mechanism as claimed in claim 1 5, in which the tape mechanism comprises two pinch rollers through which the tape may be fed.

17. A banding mechanism as claimed in claim 16, in which one roller is driven by a motor having a shaft encoder under the control of a motor drive circuit and associated control system which, in use, is used to create a servo control loop operating a speed and position control system means for controlling the position of the tape.

18. A bundler system comprising a banding mechanism as claimed in claim 15, 16 or 17.

1 9. A tape sensor substantially as hereinbefore described with reference to the accompanying drawings.

20. A banding mechanism substantially as hereinbefore described with reference to the accompanying drawings.

21. A bundler system substantially as hereinbefore described with reference to the accompanying drawings.