MEANS FOR ACHIEVING SYNCHRONIZED MOTION IN AT LEAST TWO MATERIAL TRANSPORT CONVEYOR BELTS

Abstract: Means for achieving synchronized motion in at least two material transport conveyor belts (1, 2). In order to work together for the purposes of transport these are arranged in parallel alongside one another and un run between their own pair of wheels, of which one wheel (3, 4) in each pair is arranged at one end of each belt (1, 2) and is driven by a drive motor (6) common to both belts. The remaining wheel in each pair is arranged at the other end of each belt (1, 2) and serves as a guide wheel. The means comprises detector means (17) so arranged as to generate a signal which indicates that a point on each belt (1, 2) has arrived in the sensitive zone of said detector means (17) and control devices (14) and correction devices (15) so arranged as to reduce for a short time the belt speed of the leading belt or alternatively to increase for a short time the belt speed of the trailing belt. The invention is characterized in that the means contains for at least one of the driving wheels (3, 4) a curved element (18) arranged at the periphery of the wheel. The width of this is at least as great as the width of the driving wheel (3, 4), and its thickness is a fraction of the diameter of the driving wheel (3, 4). The surface of the curved element (18) facing the driving wheel (3, 4) is similar in shape to the surface at its periphery. The curved element (18) is controlled by the aforementioned control device (14) in such a way that, in order to increased the belt speed of a trailing conveyor belt, it is brought into operative engagement with the surface of the periphery of the driving wheel and is caused to accompany the driving wheel (3, 4) in its direction of rotation, this being the equivalent of a temporary increased in the diameter of the wheel. Otherwise the curved element (18) is brought out of engagement with the periphery of the driving wheel and remains stationary at a point along that part of the periphery of the wheel which is not in contact with the conveyor belt (1, 2).

Description: Means for achieving synchronized motion in at least two material transport conveyor belts The present invention relates to a means for achieving synchronized motion in at least two material transport conveyor belts which, in order to work together for the purposes of transport, are arranged in parallel alongside one another and run between their own pair of wheels, of which one wheel in ' each pair is arranged at one end of each belt and is driven by a drive motor common to both belts, and the remaining wheel in each pair is arranged at the other end of each belt and serves as a guide wheel, said means comprising detector means so arranged as to generate a signal which indicates that a point on each belt has arrived in the sensitive zone of said detector means, and control devices and correction devices so arranged as to reduce for a short time the belt speed of the leading belt or alternatively to increase for a short time the belt speed of the trailing belt. In conveyor means of the nature indicated above, in which a number of conveyor belts work together in order to support and transport loads, it is inevitable that the belts will not run in total synchronism. One reason for this may be different rates of wear in the drive wheels, which in turn gives them different diameters; another reason may be different degrees of stretching of the belts due to uneven loading. Uneven running of the belts may cause the load to become displaced and perhaps even to fall from the conveyor belts, an event which may result in damage to the load, to the conveyor means or to individuals in the immediate vicinity of the conveyor belts. Control systems for particular applications are already available by means of which extremely precise control of the belts can be achieved such that they will run in total synchronism. In another, rather more simple previously disclosed method for achieving synchronised motion in the conveyor belts, the driving of the leading belt is interrupted at intervals by means of a coupling organ connected between the motor and the appropriate driving wheel. In the case of material transport conveyor belts which are so arranged that a component of the gravitational force of the load is parallel with the belt, what will be required during the aforementioned interval is for the belts to be braked in order to prevent the belts from adopting even poorer synchronization under the effect of the gravitational force component. The object of the present invention is to achieve by a simple and inexpensive means synchronized motion in at least two material transport conveyor belts, and this is made possible in accordance with the invention by the means containing for at least one of the driving wheels a curved element arranged at the periphery of the wheel, the width of which is at least as great as the width of the driving wheel, the thickness of which is a fraction of the diameter of the driving wheel and the surface of which facing the driving wheel is similar in shape to the surface of the periphery, said curved element being controlled by the aforementioned control device in such a way that, in order to increase the belt speed of a trailing belt, it is brought into operative engagement with the surface of the periphery of the driving wheel and is caused to accompany the driving wheel in the direction of its rotation, this being the equivalent of a temporary increase in the diameter of the wheel, although it is otherwise brought out of engagement with the periphery of the driving wheel and remains stationary at a point along that part of the periphery of the wheel which is not in contact with the conveyor belt. A preferred embodiment of the means in accordance with the invention comprises an electromagnet so arranged as to bring the curved element out of engagement with the periphery of the driving wheel against the effect of a spring, said spring being so arranged as to bring the curved element into operative engagement with the periphery of the driving wheel. 4 - and the guide wheels support rollers 13, of which only two are shown in the drawing. As mentioned by way of introduction, the belts may not run in synchronism for various reasons. This means that the material on the belts will exhibit a tendency to turn in the horizontal plane and may result in the material falling from the belts. In order to prevent the belts from pulling at different speeds, means are provided which are so arranged as to detect a certain point on each belt and to generate a signal when said point has arrived in the sensitive zone of said detector means, in addition to which a control device 14 connected to the detector means and correcting means 15 connected to the control device are provided which are so arranged as to reduce for a short time the belt speed of the leading belt or alternative.ly to increase for a short time the belt speed of the trailing belt. Which of the aforementioned control alternatives is used can vary depending on the type of transport which is to be performed. Detection may similarly be performed in different ways, including mechanically by means of so-called limit switches, optically by means of photo-cells or, as in the case illustrated in the drawing, by means of magnets 16 arranged at mutually equidistant points on the belts and detector means 17 sensitive to magnetic fields, for example the so-called reed relays which for purely practical purposes are situated adjacent to the support rollers 13 on the unit 9, but are not visible in Fig. 1. The control function may be executed in accordance with many different principles. For example, steps may be taken to ensure that one of the belts normally runs slightly faster than the other belt, and provided that the appropriate detector means are used to demonstrate that the belt is ahead of the other belt, its speed is reduced for a short time. Alternatively, the speed of the trailing belt may be increased for a short time until it is demonstrated by means of the aforementioned detector means that the normally leading belt is in actual fact the trailing belt. A - 3 - In order that the correction of the belt speed shall take place as evenly as possible, the ends of the curved element are tapered in the form of a wedge, as may be appreciated from a further individual characteristic feature of the invention. The invention is described in more detail below in connection with the accompanying drawing, which shows the invention applied to a hoist for roofing tiles. In the drawing Fig. 1 shows diagrammatically in perspective view the loading station of the hoist, i.e. the point at which the roofing tiles are loaded onto the belts. Fig. 2 shows in an oblique view from the rear details of a drive motor with two driving wheels and on one of these an embodiment of a means in accordance with the invention. The designations 1 and 2 are used in the drawing to denote two material transport conveyor belts which run in parallel alongside one another between their own pairs of wheels arranged at either end of the belts. The only wheels shown in the drawing are those which act as driving wheels 3 and 4, which are driven via a gearbox 5 by a common drive motor 6, preferably an electric motor. The remaining two wheels at the other ends of the belts 1, 2 serve as guide wheels for the belts 1, 2. The above-mentioned components, of which the wheels 3, 4, the gearbox 5 and the electric motor 6 should preferably be assembled into a single unit 9, are mounted on a frame 8 supported on wheels 7 so that the roof tile hoist can easily be transported by being towed behind a lorry, for example. The front part of the top of the unit 9 is executed in the form of a loading station for the material, in this case roofing tiles 10, to be transported by means of the belts 1, 2. At the loading station the material is placed on rails 11, and to.the belts 1, 2 there are fitted fingers 12 so arranged as to push the material off the rails so that it will eventually be fully supported by the belts 1, 2. In order to provide support for these there are arranged along the path of the belts between the driving wheels further control principle is based on the belts being made to run at the same speed. If it is,.found that one belt is ahead of the other, then either the speed of the former is reduced or the speed of the trailing belt is increased for a short time until the opposite situation exists. Other control principles are known to the specialists, although these will not be described here. In accordance with the invention the aforementioned correction means 15 comprises a curved element 18 arranged at each driving wheel 3, 4, the width of which is at Least as great as the width of the driving wheel 3, 4, the thickness of which is a fraction of the diameter of the driving wheel, and the surface of which facing the driving wheel is similar in shape to the surface of the periphery of the latter. The curved element 18 is mounted in such a way that on the one hand it is brought into engagement with the surface of the periphery of the wheel under the effect of a spring 19, and on the other hand it is brought out of engagement with said surface of the periphery under the effect of an electromagnet 20 and against the effect of the spring 19. The mounting consists of an L-shaped articulated arm 21 which is supported so that it is free to rotate in relation to the shaft 22 of each driving wheel 3, 4. On the articulated arm 21 there is arranged a yoke 23 situated coaxially with the electromagnet 20. The correction means in accordance with the invention operates in the following manner, for which purpose it is assumed that the conveyor belt 2 is trailing behind in relation to the conveyor belt 1 : under the effect of the electromagnet 20 which is supplied with current from the control device 14 and attracts the yoke 23, the curved element 18 is brought out of engagement with the driving wheel 4 against the effect of the spring 19 and remains stationary at a point on the periphery of the driving wheel 4 which is not in contact with the belt 2. By means of signals from the detector means 17:1 and 17:2 the belt 2 is found to be running ahead of the belt 1, with the result that the current supply to the electromagnet is interrupted. Under the effect of the spring 19 the curved element 18 is brought into engagement with the surface of the periphery of the driving wheel 4 and accompanies it as the wheel rotates. The effect of this is to provide the driving wheel 4 with a slightly increased circumference, which in turn causes a slight increase in the belt speed, thereby correcting the lag in the belt 2. It will be appreciated that, by the appropriate arrangement of the control device 14, it is possible to achieve by means of the invention any of the control alternatives described above. In order for the curved element 18 not to give rise to uneven operation its ends taper in the form of a wedge, and in order for the curved element to achieve reliable engagement with the surface of the periphery of the wheel the surface of the curved element which faces the aforementioned surface exhibits a friction-increasing surface structure. The invention may not be regarded as being restricted to the illustrated and specified embodiment, but may be modified within the scope of the invention in many ways with regard both to its construction and to its use.

Claims: Fatent Claims 1. Means for achieving synchronized motion in at least two material transport conveyor belts ( 1, 2) which, in order to work together for the purposes of transport, are arranged in parallel alongside one another and run between their own pair of wheels, of which one wheel (3, 4) in each pair is arranged at one end of each belt (1, 2) and is driven by a drive motor (6) common to both belts, and the remaining wheel in each pair is arranged at the other end of each belt (1, 2) and serves as a guide wheel, said means comprising detector means (17) so arranged as to generate a signal which indicates that a point on each belt (1, 2) has arrived in the sensitive zone of said detector means (17), and control devices (14) and correcting devices (15) so arranged as to reduce for a short time the belt speed of the leading belt or alternatively to increase for a short time the belt speed of the trailing belt, c h a r a c t e r i z e d in that the means contains for at least one of the driving wheels (3, 4) a curved element (18) arranged at the periphery of the wheel, the width of which is at least as great as the width of the driving wheel (3, 4), the thickness of which is a fraction of the diameter of the driving wheel (3, 4) and the surface of which facing the driving wheel is similar in shape to the surface of the periphery, said curved element (18) being controlled by the aforementioned control device (14) in such a way that, in order to increase the belt speed of a trailing belt, it is brought into operative engagement with the surface of the periphery of the driving wheel and is caused to accompany the driving wheel (3, 4) in its direction of rotation, this being the equivalent of a temporary increase in the diameter of the wheel, although it is otherwise brought out of engagement with the periphery of the driving wheel and remains stationary at a point along that part of the periphery of the wheel which is not in contact with the conveyor belt (1, 2). - 8 - 2. Means as claimed in Patent Claim 1, c h a r a c t e r i z e d in that the means comprises an electromagnet (20) so arranged as to bring the curved element C18) out of engagement with the periphery of the driving wheel (3, 4) against the effect 5 of a spring (19), said spring C19) being so arranged as to bring the curved element (18) into operative engagement with the periphery of the driving wheel (3, 4). 3. Means as claimed in Patent Claim 1, c h a r a c t e r i z e d 10 in that the ends of the curved element (18) are tapered in the form of a wedge. 4. Means as claimed in Patent Claim 1, c h a r a c t e r i z e d in that the surface of the curved element (18) facing the 15 driving wheel (3, 4) exhibits a friction-increasing surface structure. 20 25 30 35

Inventors: ANDERSSON RUNE, ANDERSSON, RUNE
Applicants: SWEDISH LIFT SYSTEM AB
Application year: 1985
Main classification: B65G23
IPC codes: B65G15, B65G23