GB2025906A - A device for detecting the presence or absence of paper or other sheets - Google Patents

Abstract

In a device for detecting the presence or absence of paper or other sheets 2, the sheets 2 are conveyed on a belt 1 in the direction of the arrow 10 over a bench 13, a fixed holder 3 supports an elastically flexible detector arm 7 carrying a detector pin 9 which rises and falls as the sheets 2 pass beneath it, an inductive pick-up 14 has a feeler element 21 engaging the arm 7, which bends up and down in accordance with the rise and fall of the detector pin 9, electric leads 18, 19, 20 carry electrical signals from the inductive pick-up 14 to appropriate amplifying and/or control and/or counting and/or other electrical apparatus. Piezo-electric or flexure sensitive resistance elements may be used to produce the electric signals from the movement of the detector, instead of pick-up 14. <IMAGE>

Description

SPECIFICATION A device for detecting the presence or absence of paper or other sheets The invention relates to a sheet detector having a detector tip p!aceable on a sheet or a sheet carrier, which tip is arranged on a detector arm mounted in a non-displaceable holder and its movement perpendicular to the sheet is convertible into an electric signal.

Such sheet detectors are necessary for example in the issuing of self-adhesive labels which are arranged at intervals from one another on a carrier sheet, from which they are detached and stuck upon any smooth underlay. The signal coming from the sheet detector is used for example for the further transport of the dispenser. It is also necessary in sheet feeders and the like to test whether a sheet is present at the moment, so that further correct processing may be initiated.

In known mechanical sheet detectors the travel of the detector tip is enlarged through a transmission lever and transmitted to a microswitch, because the micro-switch requires a relatively large switching stroke. In the case of higher switching frequency the transmission lever must be initially stressed with a large spring force, so that great friction upon the label paper must be tolerated and great traction forces are required, necessitating a high motor power and a large clutch. On account of the resulting high masses it is possible to work only with relatively low switching frequency and thus low labelling output.

In long-term operation great wear occurs on the detector tip, the life is limited by the micro-switch.

For label-edge recognition opto-electronic sheet detectors are also known which work with transmitted-light barriers or reflected-light barriers. Here one is dependent upon the transparency or the degree of reflection of the carrier paper and the label paper.

In another known form of embodiment the detector tip is pivotably mounted and connected through levers with a permanent magnet which can dip into a coil in order electrically to trip a pulse. The necessary lever linkage leads to inexact switching actions.

The invention is based upon the problem of producing a sheet detector which can be used universally and, with high switching frequency, and trouble-free operation, guarantees a high switching accuracy.

To solve this problem the invention provides that the detector tip is in connection with an active flexure element the flexure movement of which is directly convertible into an electric output value. The active flexure element can be formed as a piezo-electric flexural oscillator and consist especially of a crystal sound pick-up, preferably a stereo sound pick-up, or can form a flexuresensitive resistance element, preferably an integrated transducer, for example in the form of a silicon chip. The active flexure element preferably directly forms the detector arm, so that in this way, on account of the low mass of the system, a high detection frequency can be achieved, the application pressure force is small, the friction can be neglected. The electric switch signal is derived directly from the stroke movement.There is independence of optical and dielectric properties of the label and carrier materials, likewise of the surface structure. Beside a high labelling rate, a distinction of label commencement and label end is possible, the expense for the sheet detector itself is low, considered from the production and assembly side. The inductive and piezo-electric sheet detectors in accordance with the invention work dynamically, they deliver a relatively high output signal even on slight variations of position of the detector tip, which signal, even when the deflection is retained, dies away to zero according to an e-function. A special adjustment of the system becomes superfluous. The flexuresensitive resistance element works statically, that is the signal does not drop off to zero after a mechanical detecting jump.

For mechanical detection, in a first form of embodiment the end of a pin standing approximately perpendicular to the sheet can form the detector tip. The pin carries a permanent magnet surrounded by a differential coil. The force transmission can be favourably influenced if the detector tip is arranged on the end of an elastic detector arm mounted in a non-displaceable holder and a sensing element of the inductive pick-up engages with the arm between the detector tip and the holder. When a piezo-electric flexural oscillator or a flexure-sensitive resistance element is used, this can be formed as detector arm which is mounted in a non-displaceable holder and carries the detector tip at its free end.

Here again the detector tip can preferably be arranged at the end of a detector arm mounted in a non-displaceable holder, in which case the flexure element issues from the holder and is connected with the detector arm through a vibration transmission element.

According to a further feature of the invention the holder is made stiff to vibration, and comprises two arms, of which the one arm serves as support for the sheet to be explored and the other arm serves as mounting for the flexural oscillator.

According to a further development of the invention the detector tip protrudes from the under side of a housing which under side serves as resting surface on the upper surface of the sheet. The signal is preferably amplified through an impedance transformer, a low-pass filter, an inverter, a pulse former and a linkage.

The invention will be explained in greater.detail hereinafter with reference to examples of embodiment thereof which are illulstrated in perspective in the accompanying drawings, wherein: Figures 1 to 5 show five different formations of sheet detectors, Figures 6a to 6d show a label strip in section, with signals tripped by the sheet detector.

In the drawings, sheets 2 are arranged at intervals from one another on a sheet carrier 1. In the illustrations the sheet carrier 1 is a carrier belt with adhesive-repellant surface and the sheets 2 are self-adhesive labels detachable from the sheet carrier 1. The sheet commencement and the sheet end are to be ascertained with the sheet detector and pulses emitted by the sheet detector serve for control purposes, especially for the transport of the sheet carrier 1.

In the embodiment according to Figures 1 there is a holder 3 having two arms 4, 5 which are connected with one another so as to be stiff to vibration by means of an intermediate piece 6.

From the arm 4 a detector arm 7 issues which is formed as active flexure element 8 and carries a detector tip 9 at its forward end. The sheet carrier 1 in its movement in the direction of the arrow 10 slides over the arm 5.

In the embodiment according to Figure 2 the detector tip 9 is again situated at the end of an elastic detector arm 7 which is made fast in the holder 3. Out of this holder 3 the active flexure element 8 also extends as electric pick-up which is coupled with the detector arm 7 through a vibration-transmission element 11. In order to avoid over-bending a travel-limiting stop 12 is arranged which is connected, in a manner not further illustrated, like the holder 3, rigidly with the bench 13 at a fixed distance, on which bench the sheet carrier 1 rests and is moved in the direction of the arrow 10.

As indicated in Figure 3, it is also possible for two active flexure elements 8 to be provided in the holder 3, these being coupled through the vibration-transmission element 11 with the detector arm 7. The flexure elements 8 are inclined at 450 to the support surface of the sheet carrier 1. In this way in the case of vertical force direction the tension of the individual elements 8 can be totalled. In the case of horizontal force direction the vibration amplitude of the two signals is in phase opposition, the signals cancel one another.

The flexure elements 8 are formed by piezoelectric flexural oscillators or flexure-sensitive resistance elements. In the latter case, integrated transducers are used for preference, for example in the form of a silicon chip which flexes when the pressure is modified. Electric signals proportional to the pressure are generated by resistors which are mounted on the chip. These components can be temperature-compensated, require no subsequent recalibration and produce an amplified output signal. Beside the bar form as illustrated, the flexure element 8 can also have the form of a dish or be made in another flat form.

In the embodiment according to Figure 4 an inductive pick-up 14 is used. The detector tip 9 is situated on the end of a pin 1 5 standing approximately perpendicular to the sheet 2 and carrying a permanent magnet 1 6. The permanent magnet 16 is surrounded by a differential coil 17, so that on a vertical movement of the detector tip 9 a differential signal is available over the leads 18,19,20.

A more favourable force transmission is achieved w.ith the arrangement according to Figure 5. The inductive pick-up 14 here engages through a feeler element 21 with the elastic detector arm 7 which again carries the detector pin 9 at its free end and is made fast on the holder 3 at its other end.

In Figures Sh to Sc the signals are reproduced which are triggered by a dynamic sheet detector in the exploration of a label strip. The label strip is reproduced in Figure 6a, the sheet carrier 1 consists of a carrier strip with silicone-treated surface, on which self-adhesive labels are stuck as strips 2. When the sheet carrier 1 with the sheets 2 is moved past the sheet detector, a noise signal amplitude Z2 results as ong as the detector tip 9 rests on the sheet 2. If at the end of the sheet 2 the detector tip 9 moves downward, one obtains (Figure 6b) a high output signal 23 having a usable signal amplitude 24 which dies away rapidly according to an e-function. When the detector tip 9 is lifted by the commencement of the next label, an output signal 25 to the other side is generated. In the case of further processing of the signals through a low-pass filter and an amplifier, digital pulses are obtained such as are reproduced in Figure 6c.

Finally through a switching logic system the control signals receive the form as reproduced-in Figure 6d, which is achieved directly in the case of use of static sheet detectors, that is especially flexure-sensitive resistance elements.

Claims (16)

1. A sheet detector having a detector tip placeable on a sheet or a sheet carrier, which tip is arranged on a detector arm mounted in a nondisplaceable holder and its movement perpendicular to the sheet is convertible into an electric signal, characterised in that the detector tip (9) isXin connection with an active flexure element (8) the flexure movement of which is directly convertible into an electric output value.

2. A sheet detector according to Claim 1, characterised in that the active flexure element (8) is formed as a piezo-electric flexural oscillator.

3. A sheet detector according to Claim 1, characterised in that the active flexure element (8) is formed as a flexure-sensitive resistance element.

4. A sheet detector according to Claim 1, characterised in that the active flexure element (8) forms the detector arm (7).

5. A sheet detector according to Claim 1, characterised in that the holder (3) is made stiff to vibration and comprises two arms (4, 5) of which the one arm (5) serves as support for the sheet (2) to be explored and the other arum (4) serves as mounting for the active flexure element (8).

6. A sheet detector according to Claim 5, characterised in that the arms (4, 5) lie side by side with spacing and are connected with one another on one side by an intermediate piece (6).

7. A sheet detector according to Claim 1, characterised in that the active flexure element (8) and the detector arm (7) issue from the holder (3) and the two are connected with one another through a vibration-transmission element (11).

8. A sheet detector according to Claim 1, characterised in that a travel-limiting stop (12) is associated with the flexure element (8).

9. A sheet detector according to Claim 7, characterised in that from the holder (3) there issue two active flexure elements (8) which are coupled through the vibration-transmission element (11) with the detector arm (7) and are arranged at the angle of 450.

10. A sheet detector according to Claim 1, characterised in that the active flexure element (8) consists of a crystal sound pick-up.

11. A sheet detector according to Claim 10, characterised in that the flexure element (8) is formed as a stereo sound pick-up.

12. A sheet detector according to Claim 1, characterised in that the flexure element (8) cooperates in a manner known per se with an inductive pick-up (14).

1 3. A sheet detector according to Claim 1b2, characterised in that a dynamic sound pick-up system is used as inductive pick-up (14).

14. A sheet detector according to Claims 1, 4 and 12, characterised in that a feeler element (21) of the inductive pick-up (1 4) engages with the elastic detector arm (7) between the detector tip (9) and the holder (3).

1 5. A sheet detector according to Claim 1, characterised in that the detector tip (9) protrudes from the under side of a housing, which under side serves as resting surface on the upper surface of the sheet.

16. A sheet detector according to Claim 1, characterised in that the signal is amplified through an impedance transformer, a low-pass filter, an inverter, a pulse former and a linkage.

1 7. A device for detecting the presence or absence of paper or other sheets, constructed and arranged substantially as described with reference to and illustrated in the accompanying drawings.