GB2394820A

GB2394820A - Sensing coin diameter

Info

Publication number: GB2394820A
Application number: GB0225563A
Authority: GB
Inventors: Thapa Kagendra
Original assignee: INNOVATION TECHNOLOGY Ltd
Current assignee: INNOVATION TECHNOLOGY Ltd
Priority date: 2002-11-01
Filing date: 2002-11-01
Publication date: 2004-05-05
Also published as: GB0225563D0

Abstract

A sensor apparatus for measuring a maximum dimension of a metallic token (coin) passing there through. The apparatus comprises: an elongate magnetic flux transmission coil arranged to generate a magnetic field at a sensing point in a coin path, the transmission coil being provided on one side of the coin path; and an elongate receiver coil arranged to measure the received magnetic flux at the sensing point at another side of the coin path adjacent the elongate transmission coil. The transmission coil is substantially longer than the receiver coil.

Description

Improvements Relatine to Coin Dimension Measurement The present invention

concerns improvements relating to coin dimension measurement, and more particularly, though not exclusively to an improved method 5 of measuring the diameter of a coin as part of a process to determine the validity of that coin. Such a method is used in an improved coin validation apparatus.

The Problem: Coin Diameter Measurement The validation of metal coins has been done in many ways prior to the present 10 invention. Often a prior art mechanism will attempt to measure the diameter of the

coin or object to be validated. This historically has been done inductively by shading the space between two coils of the same size and shape, usually connected in series with each other (see MEI, (Mars) et al. for example). Alternatively, this has been achieved optically (see National Rejectors, for example) by measuring the chord of 15 the circular coin or simply by the size of the hole the coin is inserted into. In most cases, the coin is rolling down a guide slope as the measurement is taken (see Figure 1). The measuring coils are usually connected in series with each other, and form part of 20 an oscillator circuit. The measurement is based on the change in frequency and/or the change in amplitude that occurs as the coin passes through the coils. The frequency of the oscillator circuit used is in the 80 kHz to 120 kHz range. This makes the measurement dependent upon the material, thickness and its diameter. However, as a result, the diameter measurement can be confused (become inaccurate) if the coin has 25 a hole in it. The coils are usually round or elliptical in shape. The coin must also roll in a repeatable way down the guide slope.

This method of measuring using similar coils works as long as the coin does not bounce up and down or move side to side as it moves through the gap between the 30 coils. Such an arrangement gives a non-linear output. This can give problems if coins in a set are very similar in size. Also errors in measurement can be created because the coin is usually moving through this arrangement. Non-circular coins may also be very troublesome.

l Apart from the difficulties mentioned above, the chord measurement works well with round coins but not so well with non-circular coins such as a heptagonal English 50 pence piece. The optical measurement is also insensitive to the material the coin is made from. However, this may be a problem if non-metallic objects are inserted.

The Invention: To resolve the issue of linearity and to avoid problems related to coin dynamics, it has been found by the present inventor that a better diameter measurement can be taken using a sensor arrangement comprising two relatively long and thin coils. This is now 10 described with reference to a specific embodiment of the present invention.

Referring now to Figure 2, a sensor arrangement embodying the present invention for use in a coin validator is shown. The arrangement comprises two elongate sensor coils and a coin path (vertical) passing between the coils. The coils are not connected to 1 S each other. Rather, one coil acts as an independent magnetic field transmitter the other

acts as a magnetic field receiver. The magnetic flux generated by the transmitting coil

projects perpendicular to the plane of the paper as shown in Figure 2. The transmission coil is, in this embodiment, longer than the receiver coil. More specifically, the relative sizes of the coils have specifically been chosen to meet the 20 general preferred characteristic of the transmission coil being at least twice as long as the receiver coil, if possible to provide the best results.

The coin can then either drop or roll through the gap between the transmission coil and receiver coil. The arrangement may be operated vertically as drawn in Figure 2 or 25 in an alternative embodiment, at a slight angle to the horizontal with the coin rolling along a corresponding slightly inclined supporting track.

The output of the receiver coil is linearly related to coin diameter. The transmission coil has an alternating current driven through it to create a local magnetic field. The

30 receiver coil is connected directly to a high-impedance input amplifier (not shown) to detect the transmitted signal. As the coin passes between the two coils the field is

blocked. The output signal of the receiver coil peaks at the maximum diameter or dimension of the coin. The output is precise to 0.25mm and is linear with diameter of the coin. Also, the left to right position of the coin relative to the coils does not affect

\ the accuracy of measurement. If the coin has a hole in it the maximum measured dimension reflects this as well.

By operating the transmission coil at a frequency of 250 kHz or higher, the diameter 5 measurement becomes independent of the metal material the coin is made from. If a plastic or other non-conducting material is inserted the output signal is not affected.

The coils do not need to be shielded with a ferrite material either as is the case with some of the prior art.

10 Alternatively, both coils may be made of a similar length but be much larger than the diameter of the coin. In this way, the coin passes between the centres (mid points along the lengths) of the coils. However, in this embodiment, the true diameter signal to total signal is reduced considerably. To account for this, additional electronics using a sample and hold peak detector to measure the total coupling without the coin 15 is provided. This is then applied differentially with the output signal as the coin passes through the coil sensor arrangement to increase the true diameter signal range, i.e. to improve the resolution.

An important aspect of the present invention is maximum dimension measurement of 20 a metal token (coin) utilising two separate coils, where one coil is substantially longer than the other. The longer coil acting as a transmission of magnetic flux, and the shorter coil acting as a receiver of magnetic flux.

However, according to another aspect of the present invention there is provided a 25 sensor arrangement for measuring the maximum dimension of a metal token (coin) utilising two elongate separate coils, where both coils are substantially longer than the maximum possible measurable diameter of the token, one coil acting as a transmitter of magnetic flux and the other coil acting as a receiver of magnetic flux. The arrangement also comprises a sample and hold peak detector which is arranged to 30 measure the total coupling without the coin present and to create a differential measurement when the coin passes between the coils.

It is to be appreciated that coins are usually made from metal. However, it is possible to have coins made of a non-metal substance, which is impregnated with metal particles. Both these types of currency are covered by the term 'metallic token'.

Claims

l ) CLAIMS

1. A sensor apparatus for measuring a maximum dimension of a metallic token (coin) passing there through, the apparatus comprising: 5 an elongate magnetic flux transmission coil arranged to generate a magnetic field at a sensing point in a coin path, the transmission coil being provided on one side

of the coin path; and an elongate receiver coil arranged to measure the received magnetic flux at the sensing point at another side of the coin path adjacent the elongate transmission coil, 10 wherein the transmission coil is substantially longer than the receiver coil.

2. A sensor apparatus according to Claim 1, wherein the transmission coil is at

least twice as long as the receiver coil.

15 3. A sensor apparatus according to Claim 1 or 2, wherein the transmission and receiver coils are relatively thin as compared to their respective lengths.

4. A sensor apparatus according to Claim 1, 2 or 3, wherein the respective axes of the transmission coil and the receiver coil are parallel to each other and are each 20 transverse to the coin path.

5. A sensor apparatus according to any preceding claim, further comprising means for operating the transmission coil at a frequency of 250 kHz or higher.

25 6. A sensor apparatus according to any preceding claim, further comprising a high-impedance input amplifier, wherein the receiver coil is connected directly to the high-impedance input amplifier.

7. A coin validator comprising a sensor apparatus according to any preceding 30 claim. 8. A method of measuring a maximum dimension of a metallic token (coin), the method comprising:

generating a magnetic field at a sensing point in a coin path using an elongate

magnetic flux transmission coil provided on one side of the coin path; passing the token along the coin path through the sensing point; and measuring the received magnetic flux in an elongate receiver coil provided at 5 the sensing point on another side of the coin path adjacent the elongate transmission coil, the transmission coil being substantially longer than the receiving coil.

9. A sensor apparatus for measuring a maximum dimension of a metallic token (coin) passing there through, the apparatus comprising: 10 an elongate magnetic flux transmission coil arranged to generate a magnetic field at a sensing point in a coin path, the transmission coil being provided on one side

of the coin path; an elongate receiver coil arranged to measure the received magnetic flux at the sensing point at another side of the coin path adjacent the elongate transmission coil; 1 5 and a sample and hold peak detector arranged to measure the total magnetic coupling between the coils without the token present and to create a differential measurement when the token passes between the receiver and transmission coils, wherein the transmission and receiver coils are substantially equal in length 20 and are substantially longer than the maximum possible diameter of the token.

10. A sensor apparatus according to Claim 9, wherein the transmission and receiver coils are at least twice as long as the maximum diameter of the token.

25 11. A sensor apparatus according to Claim 9 or 10, wherein the transmission and receiver coils are relatively thin as compared to their respective lengths.

12. A sensor apparatus according to Claim 9, 10 or 1 1, wherein the respective axes of the transmission coil and the receiver coil are parallel to each other and are each 30 transverse to the coin path.

13. A sensor apparatus according to any of Claims 9 to 12, further comprising means for operating the transmission coil at a frequency of 250 kHz or higher.

14. A sensor apparatus according to any of Claims 9 to 13, further comprising a high-impedance input amplifier, wherein the receiver coil is connected directly to the high-impedance input amplifier.

5 15. A sensor apparatus according to any of Claims 9 to 14, wherein coin path is arranged to be located adjacent the mid-points in length of both of the transmission and receiver coils.

16. A coin validator comprising a sensor apparatus according to any of Claims 9 10 to 15.

17. A method of measuring a maximum dimension of a metallic token (coin), the method comprising: generating a magnetic field at a sensing point in a coin path using an elongate

15 magnetic flux transmission coil provided on one side of the coin path, passing the token along the coin path through the sensing point; measuring the received magnetic flux in an elongate receiver coil provided at the sensing point on another side of the coin path adjacent the elongate transmission coil, the transmission and receiver coils being substantially equal in length and 20 substantially longer than the maximum possible diameter of the token, measuring the total magnetic coupling between the coils without the token present, and creating a differential measurement when the token passes between the receiver and transmission coils.

18. A method according to Claim 17, wherein the measuring step is carried out with the use of a sample and hold circuit.

19. A method or apparatus substantially as described herein with reference to 30 Figure 2 of the accompanying drawings.