GB2147996A - Electrical measurement of the dimensions or volumes of articles - Google Patents

Abstract

For the measurement of their dimensions or volumes, objects are conveyed e.g. on a conveyor rollers 14, through a measuring frame 10 having a plurality of light sources 40 and a plurality of light detectors 41 arranged in pairs in two principal directions. The detectors 41 are adapted each to emit a signal when exposed to light from the respective light source 40. A calculating device receives and compiles the signals from the detectors and based on this information calculates the volume and/or the dimensions of the object. The light sources 40 are arranged to be switched on cyclically in sequence each for a certain time period, and the light detector 41 belonging to the same pair during the same time period, and only during the specific time period, is arranged to be able to detect light from the light source and emit a corresponding signal, which signal is transferred to the calculating unit. <IMAGE>

Description

SPECIFICATION An arrangement and a method for the measurement of the dimensions or volumes of articles This invention concerns an arrangement for the measurement of the dimensions or volumes of objects conveyed on a conveyor surface, comprising a measuring frame having a plurality of light sources and a plurality of light detectors, arranged in pairs in two principal directions, the detectors being arranged for emitting a signal when exposed to light from a light source, and a calculating device, which compiles the signals from the detectors and based on this information calculates the volume and/or the dimensions of the object.

The invention also relates to a method of carrying out general measurement of the dimensions or volumes of objects so conveyed and using such detectors and calculating device.

Varies arrangements are already known, for effecting volume measurement, incorporating light sources and detectors arranged in pairs in two directions, usually perpendicular to one another. The light beams between the light sources and the detectors form a grid over a measurement area. The volume measuring apparatus also includes some kind of transport means, which progresses objects to be measured through the measurement area. When an object to be measured passes through the measurement area, some of the light beams are interrupted and the corresponding detectors cannot register any light. Consequently signals are transferred to a calculating unit which complies the signals to a cross-section area of the object. A number of cross-section areas of the object are calculated in this way until the object has passed through the measuring area.Between each calculated cross section area there is an interval, which may be a time interval or a transport length (or movement) interval. Knowing the speed at or the distance through which the object has travelled during the measurement, also the third dimension of the object is known and can be used by the calculating unit, which compiles all the imformation to give as a result the volume and/or dimensions of the object.

However, this previously known apparatus has several drawbacks. The light sources have to be arranged at a certain distance from each other for space reasons and the detectors cannot be spaced too close to each other, otherwise one or more of the detectors may receive light from a light source other than the corresponding light source(s). Thus, it is not possible to make an accurate measurement of an object with this previously known apparatus.

An object of the present invention is so to improve and develop the previously known arrangement that more accurate measurement of an object can be made, with closer distances between the measuring lines. A further object of the invention is to provide a method of operating such an arrangement, to obtain particularly accurate measurement of an object.

Pursuant hereto the present invention provides an arrangement for the measurement of the dimensions or volumes of objects conveyed on a conveyor surface, comprising a measuring frame with a plurality of light sources and a plurality of light detectors, arranged in pairs in two principal directions, the detectors being arranged for emitting a signal when exposed to light from a light source, and a calculating device, which compiles the signals from the detectors and based on this information calculates the volume and/ or the dimensions of the object, characterised in that the light sources are arranged to be switched on cyclically in sequence for a certain time period and that the light detector belonging to the same pair, during the same time period, and only during that specific time period, is able to detect light from the light source and emit a signal indicative thereof, which signal is transferred to the calculating unit.

The invention further provides a method of measuring the dimensions or volumes of objects conveyed on a conveyor surface past a measuring frame with a plurality of light sources and light detectors arranged in pairs in two principal directions, said detectors emitting signals, when exposed to light from a light source, which signals are transferred to a calculating device, which compiles the signals from the detectors and calculates the volume and/or the dimensions of the measured object, characterised in that the light sources are switched on cyclically in sequence for a certain time period and that the light detector belonging to the same pair during the same time period, and only during that specific time period, is able to detect light from the light source and emits a signal indicative thereof, which signal is transferred to the calculating unit.

In carrying the invention into effect the arrangement includes a number of light sources, which are switched on in sequence, preferably for a very short period. The corresponding detectors are provided with a switch arrangement such that they can only transmit a signal, that they are receiving light, during the same period as the light source belonging to the same pair is sending out light. In this way, the light beams cannot spread and affect any detectors other than the one belonging to the same pair. Thus it is possible to place the detectors very close to each other.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: Figure 1 is a side view of a first embodiment of the arrangement of the invention; Figure 2 is an end view of the arrangment of Fig. 1; Figure 3 is a plan view of the arrangement of Figs. 1 and 2; Figure 4 is an enlarged section through a frame member present at the measurement area of the arrangement of Figs. 1 to 3; and Figure 5 is a perspective view of a second embodiment of the arrangement of the invention.

The embodiment shown in Figs. 1 to 3 includes a measuring frame 10 having light sources 40 and detectors 41 arranged over a transport device or conveyor 12, which in the illustrated case is a roller conveyor comprising rollers 14. The entire arrangement is mounted on a frame 1 6 having legs 18. At the outlet end of the machine at the left side of Figs. 1 and 3, there is a weighing area 20 having undriven rollers 22 forming a weighing plane and weighing machinery (not shown) built into the frame 1 6. Also provided is a safety barrier 24 for personal handling objects measured in the unit. On the frame 1 6 there is a motor control box 25.

The measurement frame 10 comprises two side members 26, 28 and a top member 30 joined together in the form of an inverted U, as well as a bottom member 32. The top member is provided with a fan 34 having an inlet opening 36 provided with an air filter. In the same way the bottom member 32 is provided with a fan 38. The function of these fans 34, 38 will be explained later. In the frame members 24, 26, 28 and 30 there are the light sources 40 and the detectors which are arranged at the inner sides of said frame members, at equal intervals. The positions of these light sources and detectors are indicated by the dotted lines 40, 41, respectively.

Fig. 2 shows how the light beams form a grid 42 in the measuring area which is provided by the frame 10.

Fig. 4 is a section through one of the frame members, showing that it comprises a supporting U-beam 44. In the interior of the Usection there is an aluminium plate 46 on which is mounted a mounting board or card 48, with the light sources 40 and auxiliary equipment, mounted with screws and distance pieces 50. The equipment on the mounting card 48 is connected to a flexible bus lead 52 and a connecting adapter 54. The bus lead 52 provides the equipment on the mounting card 48 with electric power and supplies a signal, which activates a light source on one card as well as the corresponding detector in the pair on another complementary mounting card mounted in an opposite position in an opposite frame member.In the figure the light source 40 is shown as comprising a light emitting diode 56 mounted such that it protrudes into a hole 58 in the aluminium plate 46 in alignment with a corresponding hole 60 in the U-beam.

When a signal activating this specific light source 56 is received, a light beam 62 of short duration is emitted by the light source.

The light beam is detected by a light detector 41, such as a photocell, arranged in a similar way in a respective hole in an aluminium plate and mounted on a corresponding mounting plate for the light detecting units.

Suitably, the light source 56 and the detector 41 have the same radial dimensions. such that they can each be mounted in the same size of hole. Typically, the light source and the light detector may each have a diameter of 3.2 mm and are inserted a few millimetres in the respective hole of substantially the same size or slightly bigger. The thickness of the aluminium plate may be about 1 5 mm, which gives a rigid construction and provides a narrow light beam from the light source. On the mounting card 48 there are also printed circuits (not shown) and various auxiliary electronic equipment, not shown in detail, such as amplifiers, signal designation units and other electronic components, which are known per se. This electronic equipment is only indicated schematically and has been allocated the common reference numeral 64.Preferably there are sixteen light sources or detector units mounted on each mounting card 48, which gives a favourable modular configuration for the measuring frames.

The necessary number of the cards 48, with their light sources or detector units, are mounted along the U-beams 44 over their full length and connected to the bus lead 52 by the connecting adapters 54. The number of mounting cards 48 may be selected as desired and is only restricted by the length they have to cover. If there are a great number of the light sources, light flashes may be emitted from two or more light sources at the same instant in the sequence, provided that there is a certain distance between the light sources, such that there is no risk that a light beam will be received by the wrong detector.

The open side of the U-beams in the frame members are covered by cover plates 66 which protect the mounting cards 48 and the equipment mounted on them. The U-beams 44, together with the cover plates 66 and end covers, form enclosed spaces, and the fans 34 and 38 are provided in order to ventilate and cool the heat-generating electrical equipment.

The fan 34 is connected to an enclosure formed by the top member 30 and side members 26, 28 and the fan 38 is connected to the enclosure in the bottom member 32.

The ventilation and cooling air, which is introduced by these fans, escapes through the holes 58 and 60 alongside the light sources 56 or corresponding detectors 41. The venti lation air thus will have the additional effect of preventing dust and dirt from entering the holes 58, 60 and creating obstacles for the light beams.

Measuring sequences for the light sources and detectors are started at regular intervals, which corresponds to a certain time interval or certain transport length (or distance of movement) for objects to be measured. In the embodiment shown in figures 1 to 3, this can be favourably combined with the drive of the roller conveyor. The roller conveyor is suitably driven by a gear reduction motor (not shown) connected to a chain drive for all of the rollers 14. With the aid of an angle indicator (not shown) having an output socket 67, signals are achieved for certain angle intervals for the rotation of the rollers 14, and thus for the distance of movement of an object being measured. This signal is transferred through leads (not shown) to a logic unit or a microprocessor 68.This logic unit or microprocessor 68 is connected to the light sources and detectors by way of the bus lead or bus leads 52. A signal from the angle indicator starts a measuring sequence through all the horizontal and vertical pairs of light sources and detectors in turn and signals are received by the unit 68 indicating if the light beams are obstructed by an object or not. These signals may be stored in the logic unit or microprocessor 68 or are immediately transferred to a computer (not shown), which calculates the volume and/or the shape of the object.

A measuring sequence through the side members 26 and 28 may start from the top and go downwards until one detector does not receive any light or momentary light emission form successive sources may go all the way down each of the side members for each sequence. The latter procedure is necessary for measurement of irregular objects. In the same way, a measuring sequence is performed in vertical direction from one side to the other. For simple calculations only the number of light beam absences and thus the horizontal extent of an object is registered and stored in the logic unit, and when the object has passed, the maximum measurement is transferred to the computer calculation.

Furthermore, for accurate measurement requirements, not only the horizontal extent of the object but also the distance from the side frame is recorded, i.e. the position of the object. This information is stored by the logic unit or microprocessor 68 or is transferred to the calculating unit which then can calculate the shape and volume of the object. The first method can be used for measuring the dimensions of a parcel, which is progressed through the measuring unit with one side approximately parallel to the direction of movement, and the other method can be used for calculating the size and volume of a parcel, which is moved through the unit in any direction, or for the measurement of an irregular object.

Suitably the interval (e.g. the distance moved by the object) between the measuring sequences is about one centimetre. With a preferred speed of movement of the article of 1 6 cm/sec this gives a measuring sequence cycle time of 1 6 Hz.

Fig. 5 shows a second embodiment of the arrangement of the invention schematically.

For the sake of clarity, the rollers of the roller conveyor are not shown, and its frame is only represented by its upper inner boundary 16'.

This embodiment has a modified measuring frame 10' provided with horizontal frame members 70, 72 in addition to the side members 26, 28, top member 30 and bottom member 32. Holes for the light sources 40 and/detectors 41, are indicated inside the frame member. In the figure, the weighting area 20 is also visible.

The measurement of an object passing through this unit is somewhat different from the first embodiment, since the third dimension of the object is also measured. Furthermore, in this embodiment it is not necessary to know the speed of the conveyor, which will be explained in the following.

Measuring sequences are repeated by the light sources and corresponding detectors at regular time intervals. When an object enters the measuring zone of the horizontal frame members 70, 72, it will gradually shut off the light beams as it progresses through the measuring area. From this, the speed of the object is detected and calculated by the logic unit or microprocessor or the calculating unit connected thereto. For an object shorter than the measuring length of the frame members 70, 72, the length is directly given by the number of obstructed light beams. Longer objects are measured by calculating the time, during which all the light beams are covered together with the speed of the object, which is achieved as described above. In the same way the length of an object is calculated when a part of an object is elevated over the measuring level for the horizontal frame members 70, 72.The elevated part of the object first breaks the horizontal and vertical light beams of the vertical measuring area and later the light beams of the horizontal measuring area.

The time lapse when only the light beams in the vertical measuring area are obstructed gives the length of the elevated portion of an object. As a check, the speed at which the light beams become unobstructed again can also be measured and compared to the speed at which they have been obstructed.

A special feature of the arrangement of the invention is that only one lead in the bus lead 52 is required to transfer signals indicating that light is passing (i.e. is unobstructed) for an entire group of detectors operating in the same sequence group. Suitably the sequencing is arranged such that a sequence starts at the same time for a horizontal and a vertical row of the detectors at the same time. If there are any measurements along the length of the conveyor, these preferably constitute a third sequence group. If the measuring area is very big, or the distance between the measuring lines is very short, it will be necessary to arrange the light sources and the detectors in more sequence groups in order to be able to go through an entire measuring sequence before it is time to start a new sequence.

For space reasons, it is hardly possible to have a closer distance between adjacent light sources and detectors than about one centimetre. In order to achieve a closer measuring accuracy, in the arrangement of the invention there may be additional rows of detectors offset sideways and in the measuring direction from the first row of detectors. The distance by which the second or further rows are offset sideways suitably should correspond to an even multiple of the distance which the measured object travels between two consecutive measuring cycles. The distance by which the light sources and detectors are off-set in the measuring direction preferably is such that the equidistance between all of the measuring points would be the same. For increased accuracy the holes 60 should then be narrow slits in the measuring direction, for instance one millimetre wide.

The sequencing of the light sources and detectors is suitable provided with the aid of a high frequency AC current source. The AC current suitably has a square wave form and the frequency may be, for instance, 3000 Hz.

Each cycle or period of the AC current activates a new light source and corresponding detector, which are operative only during the duration of a half cycle or period. In this way a very long sequence of measuring points can be covered during a short time period. If this is not enough for the measurement requirements more measuring circuits with the same frequency can be arranged for the frequency can be further increased.

In the arrangement according to the invention, the mounting cards with the light sources and the mounting cards with the detector units can be exchanged with one another, because they are both activated by the same starting impulses. This offers the possibility of arranging light emitting and light detecting cards so as to alternate along the length of a frame member. This will give a more even heat development in the frame members, since the heat developed by the cards containing the light sources and the cards containing the detectors is different.

In carrying the invention into effect it is of course possible to carry out the measurements in more than two directions by arranging more than one measuring frame on the apparatus or to provide a further off-set system of light sources and detectors, with the light beams extending at an oblique angle to the frame. The number of such oblique measuring directions can, of course, be adapted to the needs of the specific measuring task which is to be performed in the measuring apparatus.

In this way also the volume and shape of the irregular objects can be measured. However, in the majority of cases objects to be measured are rectangular and in many other cases it is the maximum dimensions which are important.

For the purpose of the invention, the characteristics of the light emitted from the light sources are arbitrary and such light may be visible or visible, and either monochromatic or not. For cost reasons, a low cost and low power-consuming light source is preferred such as a light-emitting diode.

The invention is not limited to the embodiments shown in the figures and described in the foregoing specification, but can be varied at will within the scope of the following

Claims (9)

claims. CLAIMS

1. An arrangement for the measurement of the dimensions or volumes of objects conveyed on a conveyor surface, comprising a measuring frame with a plurality of light sources and a plurality of light detectors.

arranged in pairs in two principal directions, the detectors being arranged for emitting a signal when exposed to light from a light source, and a calculating device, which compiles the signals from the detectors and based on this information calculates the volume and/or the dimensions of the object, characterised in that the light sources are arranged to be switched on cyclically in sequence for a certain time period and that the light detector belonging to the same pair, during the same time period, and only during that specific time period, is able to detect light from the light source and emit a signal indicative thereof, which signal is transferred to the calculating unit.

2. An arrangement as claimed in claim 1, characterised in that the measuring sequences are started at regular time intervals.

3. An arrangement as claimed in claim 1 characterised in that measuring sequences are started at regular intervals for the conveyed distance of the object.

4. An arrangement as claimed in claim 1, 2 or 3 characterised in that the output signals from a plurality of light detectors are transmitted through the same lead to a microprocessor or logic unit.

5. An arrangement as claimed in any preceding claim, characterised in that the light sources and the light detectors are arranged in a measuring frame comprising U-beams having holes for the passage of light beams.

6. An arrangement as claimed in claim 5, characterised in that the U-beams are covered at their open sides by cover plates and at their ends to form enclosed spaces, and that fans are provided to supply clean air to said enclosed spaces, air exits from said enclosed spaces being through the holes.

7. A method of measuring the dimensions or volumes of objects conveyed on a conveyor surface past a measuring frame with a plurality of light sources and light detectors arranged in pairs in two principal directions, said detectors emitting signals, when exposed to light from a light source, which signals are transferred to a calculating device, which compiles the signals from the detectors and calculates the volume and/or the dimensions of the measured object, characterised in that the light sources are switched on cyclically in sequence for a certain time period and that the light detector belonging to the same pair during the same period, and only during that specific time period, is able to detect light from the light source and emits a signal indicative thereof, which signal is transferred to the calculating unit.

8. An arrangement for measuring the dimensions or volumes of objects substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 4 or in Fig. 5 of the accompanying drawings.

9. A method of measuring the dimensions or volumes of objects substantially as hereinbefore described with reference to the accompanying drawings.