The invention relates to a method and a device for testing coins, in which the image of the coin is detected using an image sensor.
In the process of recognising the embossing on coins there is a known way of using photographic image sensors which usually have pixels arranged in columns and lines. Here it is necessary to determine the correct moment of the recording of the moved objects i.e. the coin (here the term “coin” is used to denote also tokens or counters or the like). One problem is detecting the coin in its unrestricted course of movement and monitoring the run of the coins only with the image recording system present or the image sensor. During the dynamic behaviour of a coin as it passes an image sensor and the production of an image by the optical image sensor, exact analysis of the times of passing through the imaging area and the recording speed of the sensor must be made. It is crucial to determine the correct value for the exposure time and the moment of the recording. Although it is possible in special cases, it is not to be expected that the coin will move through the recording area of the image sensor at a constant speed and certainly will not stay there for a short time at all. There are four time areas to be examined, namely the run-in of the coin into the sensor area, the recording/exposure time, the data transfer or transmission for processing the image in an evaluation device and the image processing, analysis and evaluation. Whilst for the fourth time period no fixed time value is given, apart from the maximum time of the entire process, the first three time periods are extremely time-critical.
Run-in times for selected coins were determined, the run-in time being determined as the time from the appearance of the edge of the coin in the recording area of the image sensor up to complete detection of the coin by this recording area. The measured run-in time was between 4.5 and 9.9 ms and that of 0.01, 0.10, 1 and 2 Euro coins was respectively 4.9, 5.9, 6.99 and 7.71 ms. The aimed-at diameter range of the coins to be measured is between 15 mm and 33 mm. Measurements in real coin checkers produced a maximum coin speed of 3 m/s. With the given time conditions it is inconceivable to follow the run of the coin up to the correct recording position by cyclical scanning of the image. Moreover in such a case the data transfer times from the image sensor to the operating processors is much too long.
The object underlying the invention is to create a method and a device for testing coins using an image sensor to record an image of the coin to be tested, in which the moment of the recording of the image of the coin or respectively the location of the recording is reliably determined and with which the data transfer times from the image sensor to the evaluation device are minimised.
This object is accomplished according to the invention by the features of the main claim and the subordinate device claim.
The invention exploits the capability of image sensors to select just partial areas. Since the scanning speed of the individual pixels is independent of their number, the transfer speed can be assumed practically proportional to the number of points to be selected. Because only at least one front column in the direction of movement of the coin and/or at least one line of the image sensor detect parameters of the coin, which together with the temporal detection information provide information about the movement of the coin, and because in dependence on these parameters and the temporal information it is determined when the coin will appear in a coverage area, desired for recording, of the image sensor, the image sensor being switched into activation of the columns and lines of the coverage area and the recording being triggered, it is possible to monitor the movement of the coin and to calculate exactly the moment of the actual recording of the image of the coin, and as a result of the activation of only the coverage area of the coin with the image sensor, the time for reading out the image data is reduced.
Advantageous developments and improvements are possible due to the measures quoted in the subordinate claims.
Through detection the apex of the coin by the at least one front column in the direction of movement, the diameter of the coin can be determined, via which information can be provided about the height and width of the coverage area.
By scanning the front edge and the apex of the coin and the temporal information of the scanning and the diameter of the coin, the speed of the coin can be calculated in a simple manner, and especially in the case of small coins which run slowly this speed information is already sufficient to fix the moment of the recording, since the recording area of the image sensor is somewhat larger than the coin surface and thus running out of the sensor area without being checked is unlikely.
It is especially advantageous, after detection of the apex of the coin, to activate at least one line of the image sensor at the level of half the diameter, and to scan the front edge of the coin a number of times, since the speed and/or the acceleration of the coin can be calculated exactly as a function of the scanning times and the distances covered. Thus the recording moment can be determined exactly even if the coin experiences a delay or acceleration in the course of its run-in.
It is advantageous that as the coin runs through the at least one column, the height pattern of the coin is detected and evaluated, grooves being recognised where discontinuities are present in the height pattern.
An illumination device is advantageously provided which is activated in a pulsed manner at the moment of the recording, and thus good illumination can be achieved as a result of the fixing of the moment of the recording, it being possible to determine the length of the illumination as a function of the speed of the coin.
Embodiments of the invention are represented in the drawings and are explained in greater detail in the following description. The figures show:
The device according to the invention is installed in a coin checker, preferably in the coin channel, in which the other measuring systems of the coin checker are also present, and the described device can be configured as a sub-system of the coin checker control system. The device has an image sensor, the term “image sensor” being intended to cover the entire recording device with lens system. In addition, an illuminating device is provided which is associated with the image sensor and which has a flashlight function, i.e. generates pulsed illumination of the coin surface.
A device according to the invention is represented schematically in
So that an assessable recording of a coin 5 can be achieved, the moment of the recording, based on the movement parameters of the incoming coin 5, must be determined via the evaluation unit 3 at the desired measuring position or at the desired recording location. To this end, in the preferred embodiment at the beginning of the detection only the first column 7 of the image sensor 2 in the direction 6 of movement of an incoming coin 5 is activated, the pixels of this first column 7 being continuously read out by the evaluation unit 3 and the run-in of the coin being awaited. As the coin 5 enters the image sensor, the front edge is detected by the column 7 and recognised by the evaluation unit 3, which activates a height check which is intended to recognise the apex of the coin.
On reaching the apex, according to
At this point in time, a first assessment of the run-in speed of the coin is possible since a speed can be calculated from the moment of scanning the front edge, the moment of scanning the apex and from the diameter. In the simplest case, i.e. if certain indistinctness is admitted, this information is already sufficient to fix the moment of the recording, which can be calculated from the speed and the desired measuring position. This is true in particular for small coins which run slowly, since the desired recording area 8, represented in broken lines, in this case covers most of the coin surface and thus the coin is unlikely to exit from the sensor area without being checked. If however it is to be expected that the speed will alter as the coin runs in, additional checking of the passage of the coin is necessary.
For this additional checking of the passage of the coin, reference is made to
Depending on the coin size, the coverage area or recording area is limited by the evaluation unit 3 triggering the lines and columns, the time for reading out the image data being reduced to a minimum. If the evaluation of the data is matched to this, in order to save space in the working memory, even the areas of the coverage area 10 which are located outside the circular image can be suppressed, i.e. the signals from these areas are not passed on by the evaluation unit 3.
During the recording according to
The illumination for the recording can take the form for example of a plurality of light diodes arranged in a ring with a diffuse reflector.
According to present knowledge, the exposure time of the recording must be controlled with the aid of deliberate control of the illumination. This is necessary since circulating coins have a very strong spectrum of contamination and oxidation and thus reflection capability. Furthermore, for cost reasons, a lens system with a fixed aperture is usually used.
On account of the expected high running speed of the coin, controlling exposure by the exposure time has to be excluded if possible. The exposure must be kept as short as possible in order to avoid movement blurs. There remains the possibility of controlling the current supply to the illumination elements or to a gain control of the image sensor.
In addition to the illumination for the actual recording, illumination for checking the coin run-in is required, which can be configured as point-source or linear illumination with a lower light intensity or energy than the main illumination in that area.
Independently of the demands on the illumination for recording the coin, therefore other illumination techniques can be used in the run-in area, by means of which additional measured values can be obtained, e.g. flat directional, in order to ascertain embossing depths with shadow formation, multi-coloured illumination for recognising two-coloured coins, coloured illumination for recognising the material.
It must also be considered that the illumination for the run-in check has to be activated a number of times if not even constantly over the entire period of the coin run-in.
Naturally this illumination for the run-in check is controlled by the evaluation unit 3, which basically monitors the run-in. Here it can also determine the average brightness of the coin which is used for controlling the exposure.
In certain circumstances, the method can be simplified to remove the recording time by additional checking of the passage of the coin as per
As a support to the run-in check in the first column, a column within the scanning area 8 can also be scanned. The time of reaching this position can then be used together with the spacing of the columns in determining the speed.
In certain cases, especially when the diameter ranges of the coins to be detected are similar, monitoring only via one line can be envisaged. But with this monitoring there is the problem of fixing the correct position of the line to be scanned. Therefore a compromise has to be made in respect of precision. Otherwise in this method also the front edge and the rear edge of the coin are detected, it being possible to determine the central position of the coin with this information. In this type of scanning, a larger scanning area of the image sensor is necessary.
There also exist image sensors which do not admit any freely positionable selection of image data, but which make possible reading of pixels in blocks or switching down to a much smaller resolution. In these cases too, the previously mentioned scanning by means of columns and possibly lines can be carried out, the columns and lines then having a reduced number of pixels.
In
As shown in
An expanded form having two adjacent columns 7, 12 simplifies the recognition of a groove since then two adjacent pixels respectively supply two negated signals. Their change shows the presence of milling on the edge of the coin 11. For the sake of simplicity, in
Number | Date | Country | Kind |
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103 07 754.5 | Feb 2003 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP04/01600 | 2/19/2004 | WO | 11/4/2005 |