GB2165515A

GB2165515A - Conveyor

Info

Publication number: GB2165515A
Application number: GB08524359A
Authority: GB
Inventors: Seiji Ishikawa; Hirishi Hashimoto
Original assignee: Mitsubishi Kasei Corp
Current assignee: Mitsubishi Kasei Corp
Priority date: 1984-10-12
Filing date: 1985-10-02
Publication date: 1986-04-16
Also published as: GB8524359D0; DE3536151A1

Abstract

A conveyor (1) for conveying one or more objects (4), in a predetermined sequence and in an intermittent mode, to a predetermined location via a selected route comprises one or more trays (2) for supporting the objects, each tray having a recess (21) in its bottom plate (22) and having a permanent magnet (23) attached thereto. A pressure vessel has an upper plate (11) with a series of holes (111) therethrough. Gas, such as air, is fed into the vessel from a gas supply (15), so that gas issuing from the holes causes the trays to float above the upper plate. Electromagnetic means (3) for generating a shifting magnetic field is arranged adjacent the bottom plate of the pressure vessel and along the selected route, to cause the trays to move by interaction between the shifting magnetic field and the permanent magnets. <IMAGE>

Description

SPECIFICATION Conveyor This invention relates to a conveyor, and more specifically to a conveyor for use in an automatic machine, for example an automatic sample feeder for an automatic chemical analyzer, an automatic chemicals feeder for an automatic chemicals/paint blender, an automatic medicine distributor/packer, an automatic liquid bottler, an automatic bottle washer, etc.

Such automatic machine requires that a plurality of containers having identical shape/dimensions, for example beakers, flasks, capsules, bottles etc.

are conveyed, in a predetermined sequence and in an intermittent mode, to a predetermined location at which a process operation specific to one of the above-identified automatic machines is conducted.

It is noted that the plurality of containers is required to be initially fed to, or loaded on, the machine at one time as a group, before each of them is conveyed in a regular sequence to the location at which the operation is conducted.

The fundamental requirements for a conveyor for use with the above-identified automatic machines are itemised below: 1. it should be simple in structure, preferably having no movable members, 2. it should be small in dimensions, weight and inertia, 3. it should have flexibility/versatility in selecting a route through which containers are conveyed, 4. it should provide accurate regulation in the positioning (stopping) of each container, 5. it should provide smooth acceleration, stable speed conveying and smooth deceleration of the containers, 6. it should have a high utilisation rate of the area of a table on which the containers are loaded to be moved along the surface thereof for conveying to the location at which the process operation is conducted, in a predetermined sequence, 7. it should be easy to operate and maintain.

In the prior art, belt conveyors and turntables are predominantly employed for conveying articles for the above-identified automatic machine.

A belt conveyor was initially developed to be employed for an assembly line in which members or parts (hereinafter referred to as an object to be carried or simply as an object) are loaded on and/ or unloaded from the belt conveyor at arbitrarily selected locations. As a result, a belt conveyor employed for the above-identified automatic machine has drawbacks as itemised below: 1. it is complicated in structure, with a large movable system comprising one or more belts and drives therefor, having a considerable weight and inertia, 2. it is complicated in operation and maintenance, 3. it is non-flexible in selecting a route through which an object is conveyed, 4. it has a relatively large positioning error due to its large inertia.

A turntable is a conveyor comprising a rotatable table on which objects are arranged around its periphery. A turntable employed for the above-identified automatic machine cannot sufficiently utilise the area of the rotatable table, due to the inherent structural limitation, in addition to the above itemised drawbacks.

Furthermore, neither a belt conveyor nor a turn table allows reciprocative operation. In other words, they do not allow a free selection of the direction in which the objects are carried.

In conclusion, none of the carriers available in the prior art is satisfactory for use with such automatic machines.

An object of the present invention is to provide an improved carrier for conveying objects in a predetermined sequence and in an intermittent mode, to a predetermined location through an arbitrarily selected route.

According to the invention there is provided a conveyor comprising at least one try for supporting an object to the conveyed, the tray having a recess in its underside and having a permanent magnet attached thereto so that a pole thereof is directed downwards; means for floating the tray, comprising gas distribution means including a plate with a plurality of holes therethrough, the holes being so positioned as to ensure that the tray always covers at least one of the holes, and gas supply means for feeding gas to the distribution means so that gas issuing from the holes causes the tray to float; and means for generating a shifting magnetic field to link with the permanent magnet, the generating means being arranged along the route along which the tray is to be moved.

In other words, the conveyor of this invention comprises basically a combination of a gas jet floating system and a linear motor.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a schematic drawing for explaining the operation of a conveyor in accordance with the invention; Figure 2 is a schematic diagram of a conveyor in accordance with a first embodiment of the invention; Figure 3 illustrates the waveforms of a progressive intermittent unidirectional current which is supplied to a linear array of electromagnets forming a linear motor of the conveyor of Figure 2; Figure 4 is a schematic diagram of a conveyor in accordance with a second embodiment of the invention; Figure 5 illustrates waveforms of a 2-phase alternating current which is supplied to a linear array of electromagnets forming a linear motor of the conveyor of Figure 4;; Figure 6 is a schematic diagram of a conveyor in accordance with a third embodiment of the invention; and Figure 7 is a plan view of an automatic chemical analyser provided with a conveyor in accordance with the invention.

Referring to Figure 1 of the drawings, a gas jet floating system comprises a pressure vessel 1 which is fabricated with an upper plate 11 of a non-magnetic material, and a lower plate 12 of a non-magnetic material, and a lower plate 12 of a non-magnetic material and a side wall 13 which is connected to an edge 112 of the upper plate and an edge 121 of the lower plate. Preferably the side wall 13 projects above the plate 11 to retain trays 2 on the upper plate 11 (as in Figure 2). The upper plate 11 has a set of holes 111 which are connected to a gas supply 15, for example an air pump, through a space 14 within the pressure vessel.It is important that the pitch of the holes 111 be selected to allow each tray 2 to cover at least one of the holes 111 so that the air pressure is applied to a shallow recess 21 in the bottom of the tray, regardless of the location of the tray relative to the upper plate 11 of the pressure vessel.

The recess 21 is provided in the lower surface of the bottom plate 22 of the tray 2 to retain the gas which has penetrated upwardly through the holes 111, thereby enhancing the floating effect, and to decrease the area with which the tray 9 contacts the upper plate 11, thereby decreasing the friction between the tray and the upper plate.

Although the essential limitations to satisfy the requirements are rather complicated, an interval between the holes 111 smaller than the length of the side (or diameter) of the bottom plate of the tray 2 may be roughly taken to be a reasonable limitation, but the dimensions of the holes 111 and of the recess 21 beneath the bottom plate 22 of the tray, or the thickness of the side wall of the tray, must be taken into consideration. In plan, the tray is preferably square or rectangular.

Each tray supports an object 4 which is to be conveyed (indicated by a broken line). Each tray is floated by the gas pressure applied to the lower surface of the bottom plate 22, caused by the gas flowing into the recess 21 of the tray from the pressure vessel 1 through the holes 111.

It is important that the recess 21 of each tray faces at least one hole 111 of the upper plate 11 of the pressure vessel, to make sure that the recess of each tray is supplied with gas through the hole 111 to ensure that the tray 2 floats without fail.

A surge tank 16 (Figure 2) is preferably arranged between the open space 14 and the gas supply 15, for the purpose of stabilising the air pressure to be applied to the recess 21 and to decrease the pressure drop between the gas supply and the recess.

It is preferable that the thickness or the vertical dimension of the pressure vessel be as small as possible, because it is in the path of the magnetic flux generated by a shifting magnetic field generating means 3 which will be described below.

A linear motor forms the magnetic system 3 for generating a shifting magnetic field, the system being arranged along the lower plate 12 of the pressure vessel 1, and also along the route over which the tray 2 is scheduled to be moved. A respective permanent magnet 23 is located beneath, or is embedded in, the bottom plate 22 of each tray. Although it is preferably that the permanent magnet 23 is arranged at the lower surface of the bottom plate 22, this is not essential. However it is important that each pole of the permanent magnet 23 is directed toward the corresponding pole of the shifting magnetic field generating means 3.A magnetic force is effective between the shifting magnet field and the permanent magnet 23 to cause the permanent magnet, together with the tray attached thereto, to start moving, to keep moving, to stop or to remain stationary, as required, in response to regulation of the speed of movement of the shifting magnetic field.

It is to be noted that the shifting magnetic field is preferably uniform, so that it readily causes accurate and smooth regulation of the movement of the tray. The linear motor, particularly when operating with a uniform shifting magnetic field, enables the tray 2 to stop and to remain stationary at an arbitary location with excellent accuracy, in response to a sustained or stationary condition of the magnetic field.

The supply of electric power to the linear motor can be suspended during a period in which the tray is kept stationary at a location. This is effective to secure the sustaining of the tray, as well as reducing the power consumption. It will be apparent that if suction is applied to the pressure vessel, this will be effective to attract the tray at a location, to keep it at that location.

A wide variety of configurations is available for the linear motor, and some examples are given below.

Referring to Figures 2 and 3, one configuration comprises a linear array of electromagnets comprising spaced-apart pole pieces projecting from a common yoke 36 arranged along the required route of the shifting magnetic field. The magnets are excited by applying DC thereto in a regular sequence. The magnets 31, 32 and 33 are arranged in groups, the magnets of each group being interleaved with magnets of the other groups, in sequence, along the route.

The shifting magnetic field generating means 3 is preferably confined in a housing 35 extending along the pressure vessel 1, the housing being effective to protect the generating means from possible contamination which otherwise could occur due to penetration of liquid or powder chemicals through the holes 111 into the space 14.

It would, of course, be possible to arrange the electric magnets in the pressure vessel 1 instead of in the housing 35 but a further drawback would result, in that the capacity of the pressure vessel would need to be larger, and this would act against easy regulation of the air flow penetrating the upper plate.

The magnets 31 are connected in series between supply lines U and U'. The magnets 32 and 33 are likewise connected between supply lines V, V' and W, W', respectively. The energisation of the groups is progressively intermittent, as shown in Figure 3.

Each set of a magnet 32 and magnets 31 and 33 adjacent thereto corresponds in length to the length of the magnet 23. A free selection is allowed for the waveforms of the progressive inter mittent DC current. Namely, not only a triangular wave, as shown, but also a trapezoidal or trapeziform wave, or a rectangular wave, etc. can be used.

In operation of the conveyor, trays 2 are placed on the upper plate 11 of the pressure vessel and the supply 15 is operated to feed air pressure into the recess 21 of each tray, via the surge tank 16, the open space 4 and the holes 111 in the upper plate 11, to float the tray so that it is held off the upper plate. The supply lines U-U', V-V' and W-W' are supplied with a progressively intermittent DC current in a regular sequence, as shown in Figure 3, causing the tray to move along the linear array of electric magnets.

It should be noted that the speed of movement of the tray can be regulated by adjusting the frequency of the current pulses. It is important that this frequency regulation is simultaneously applied to the currents fed to all three supply lines. As a result, the tray can be stopped and kept stationary, by sustaining each supply pulse at a desired point in time or at a desired location, regardless of whether the tray directly faces any of the poles.

This is clear from the conventional theory of the shifting magnetic field.

In response to the holding of the current at a constant level, the tray stops, but is kept floating due to the air flowing into its recess 21 through the holes of the upper plate. Thereafter, if the supply of air is arrested, or if suction is, instead, applied to the pressure vessel, so that the tray sits firmly on the top plate, the supply of current to the electromagnets can be ceased whilst the trays are to remain stationary. The intensity of the electric current and the polarity of the electromagnets at the time of stopping may be memorised by an electric current regulator (not shown). When the tray is to be moved again, the electromagnets are then supplied with an electric current having the intensity and polarity which were memorised earlier by the electric current regulator. The supply of air is then resumed to float the tray.After the tray has become stable, the intensity of the electric current is changed, to cause the required movement.

This example may be considered as a linear motor driven by a polyphase AC supply 100% biased to either plus or minus potential. Although the above description relates to a 3-phase configuration, 4- or 5-phase supplies may be more convenient, depending on the relationship between the dimensions of the tray 2 and the dimensions of the electromagnets.

Referring to Figures 4 and 5, in a second example of a linear array of electromagnets arranged along the required route of the shifting magnetic field, the magnets are excited by an alternating current in a regular sequence along the route of the shifting magnetic field. In this case, there are four groups of electromagnets 31, 32, 33 and 34, four adjacent electromagnets 31 and 33 are connected together in series between supply lines U and U', and likewise the magnets 32 and 34 are connected between lines V and V'. The connections to the magnets 33 and 34 are reversed relative to those of the magnets 31 and 32, to cause the magnets 31 and 32 to be magnetised with the opposite polarity to the magnets 33 and 34.

This example may be considered as a linear motor driven by a polyphase AC supply. Although the above description refers to a 2-phase supply, a 3phase supply might be more convenient, or a 4- or 6-phase supply might be employed. In fact, any desired number of phases may be used. Again, the waveform may be triangular, as shown in Figure 5, rectangular, trapezoidal, trapeziform, or any other suitable waveform.

Referring to Figure 6, in the third example a 3phase winding energised by a normal 3-phase sinusoidal alternating current is provided for generating the shifting magnetic field, in place of the linear array of electromagnets. This would be the preferred arrangement, because in this configuration it is easy to produce a uniform shifting magnetic field and it is easy to regulate the acceleration, the stable-speed movement and the deceleration of the tray 2. It is to be noted that accurate positioning or stopping of the tray at an arbitrary location is quite easy.

Although Figure 6 does not indicate the mutual connection of the coils in the upper and lower parts of each slot, it will be clear to any person skilled in the art that Figure 6 shows an example of a normal 3-phase AC winding arrangement for generating a shifting magnetic field which is produced by coils inserted in double layer slots. It will also be clear that such 3-phase winding for generating a shifting magnetic field is usually a loop.

Therefore, Figure 6 can be taken as showing a part of the loop, and that the right hand end of the winding shown in the drawing is eventually connected to the left hand end of the winding through pole-sectors represented by U, V and W.

Regardless of the style of linear motor employed, the plan-view of a conveyor in accordance with the invention, applied to an automatic chemical analyser, may be as shown in Figure 7.

Referring to Figure 7, an automatic analyser module 5 is arranged at a desired location alongside the conveyor. In order to conduct automatic chemical analyses sequentially on a plurality of samples contained in containers 4, for example beakers, flasks, capsules, or bottles, (shown in broken lines), the containers 4 are placed on respective trays 2, which are located on the upper plate 11 of the pressure vessel 1. Although the trays in Figure 7 are shown as circular, as was described earlier the trays are preferably square or rectangular, because such shape improves the utilisation of the gas employed in the gas jet floating system.

Application of air pressure to the recess 21 of the trays 2 causes the trays to be floated. In response to the movement of the shifting magnetic field generated by the linear motor, the trays are moved in a regular sequence along the route shown by an arrow A, in an intermittent mode, to allow the automatic analyser module 5 to conduct analysis of each of the samples in a regular sequence. It will be apparent that by suitable choice of the current waveforms, the trays can be made to move, alter natively, in the opposite direction. The layout of the route along which the trays are moved, and the area of the table, can be selected as required. In other words, it is an entirely free choice whether or not the entire surface or a part of the surface of the conveyor is utilised. However, even in the case where a part of the surface of the conveyor is utilised, it is preferable to allow all of the holes to be covered by the trays, because this economises in the gas which is employed for floating the trays.

Claims

1. A conveyor comprising at least one tray for supporting an object to be conveyed, the tray having a recess in its underside and having a permanent magnet attached thereto so that a pole thereof is directed downwards; means for floating the tray, comprising gas distribution means including a plate with a plurality of holes therethrough, the holes being so positioned as to ensure that the tray always covers at least one of the holes, and gas supply means for feeding gas to the distribution means so that gas issuing from the holes causes the tray to float; and means for generating a shifting magnetic field to link with the permanent magnet, the generating means being arranged along the route along which the tray is to be moved.

2. A conveyor as claimed in claim 1, wherein the shifting magnetic field generating means comprises an array of DC electromagnets; wherein the electromagnets are arranged in a plurality of interleaved groups, a set of adjacent electromagnets comprising one from each group substantially corresponding in length to the dimension of the permanent magnet; and wherein the groups of electromagnets are excited in a regular sequence.

3. A conveyor as claimed in claim 1, wherein the shifting magnetic field generating means comprises a linear array of polyphase AC electromagnets.

4. A conveyor as claimed in claim 1, wherein the shifting magnetic field generating means comprises a poly-phase AC winding.

5. A conveyor as claimed in any preceding claim, wherein the plan-view of the or each tray is a square or a rectangle.

6. A conveyor as claimed in any preceding claim, wherein the spacing between adjacent ones of the holes is smaller than the width of the tray.

7. A conveyor as claimed in any preceding claim, wherein the distribution means comprises a pressure vessel; and wherein the plate forms the top of the pressure vessel.

8. A conveyor substantially as hereinbefore described with reference to the accompanying drawings.