WO2005109111A1

WO2005109111A1 - Conveyor belt system

Info

Publication number: WO2005109111A1
Application number: PCT/GB2005/001522
Authority: WO
Inventors: Sarah Bee
Original assignee: Sortex Limited
Priority date: 2004-05-06
Filing date: 2005-04-20
Publication date: 2005-11-17
Also published as: GB0410136D0

Abstract

A conveyor belt system is disclosed in which a belt (2) extends around two rollers (4, 6) spaced by a distance equal to or less than the width of the belt. In order to adjust the tension in the belt (2) and its lateral position on the rollers (4, 6) one of the rollers is movable by means of two actuators (8, 10) each operable to move an end of the one roller (6) relative to the other roller (4). The system includes a position sensor (20) for monitoring the lateral position of the belt (2) and a load sensor (18, 22) for monitoring the belt tension. The sensors transmit signals to a control unit (16) which instructs the actuators (8, 10) to move the roller (6) to compensate for any excessive lateral movement of or tension changes in the belt (2).

Description

CONVEYOR BELT SYSTEM

This invention relates to conveyor belt systems and particularly to the tracking of conveyor belts used in sorting machines. The invention is especially concerned with systems in which the width of the conveyor is equal to or greater than its length. A sorting machine that uses such short conveyors is described in our United States Patent Nos: 5 538 142; and 6 056 127.

In systems where the conveyor length is longer than its width, self tracking is possible with crowned rollers at either end. With short conveyors, where the width is greater than the length, this is not possible.

The materials used in conveyor belts can shrink or stretch over time, leading to increased or decreased tension in the belt in the absence of adjustment. If adjustment is available, this does have to be properly monitored in order to avoid premature failure of components or decreased tension preventing consistent product feed. Temperature and load differentials across and along a belt also create irregular tension which has to be compensated to avoid belt mistracking during product feed. This is particularly relevant to conveyor systems carrying product at different temperatures, and in sorting machines where the product on the conveyor can be fresh or frozen.

The present invention is directed at a short conveyor belt system, in which a belt extends around two rollers spaced by a distance equal to or less than the width of the belt. In a system of the invention the ratio of belt width to conveyor length is normally in the range 1.2 to 2; preferably around 1.5. A typical belt width in systems in which the invention can be exploited is around 1250 mm. A typical belt for use in systems of the invention is a polyurethane, single ply belt, about 1.5 mm thick. According to the invention one of the two rollers in the conveyor system is movable by means of two actuators, each operable to move an end of the one roller relative to the other roller. The system includes a position sensor for monitoring the lateral position of the belt, and a load sensor for monitoring the tension in the belt. A computer receives signals from the sensors, and operates the actuators in response thereto to position the movable roller to maintain the tension in the belt in a desired range, and the belt in a correct lateral position on the rollers.

In a belt system according to the invention the position sensor is typically a proximity sensor focusing on an edge of the belt between the rollers. A preferred sensor is an ultrasonic proximity sensor. It can be focused on the actual edge of the belt, or on markings such as a continuous line in a marginal edge section of the belt. The sensor can be programmed to monitor lateral movement of the belt edge in either direction and transmit a signal to the computer whenever the edge goes beyond a specified range. Alternatively, the sensor can generate a continuous signal representative of the position of the belt edge, the signal being transmitted to the computer. The computer can then be programmed to operate the actuators as appropriate, when the signals from the sensor indicate lateral movement of the belt edge beyond the desired range. This arrangement makes it possible to alter the desired range at the computer if this is required, without any adjustment at the sensor being needed.

The specified or permitted range of lateral movement may be very small; relative to the width of the belt eg, of the order of 1%. In short belt systems in which the belt runs at high speeds, preferably only a very low level of lateral movement should be tolerated.

The load sensor typically comprises a load cell or strain gauge monitoring the force applied by the belt to one of the rollers at at least one end thereof. Normally the applied force will be monitored at each end of one of the rollers, and the force applied to the movable roller that is most easily monitored. This enables each load cell to be coupled to one of the actuators to monitor directly the active force generated in the actuator to hold the movable roller against the belt tension.

Further features and advantages of the invention will be apparent from the following description of embodiments thereof, in which reference will be made to the accompanying schematic drawings wherein:

Figure 1 is a diagrammatic representation of a conveyor belt system embodying the invention; and

Figures 2A and 2B show an alternative belt and roller configuration.

The conveyor belt system shown in Figure 1 comprises a polyurethane, single ply belt 2 extending around a first roller 4 fixed in a frame (not shown) and a second roller 6 movably mounted on the frame. The second roller 6 can be a crowned roller, to provide some additional stability. The second roller 6 is held at its spacing from the first roller 4 by actuators 8,10. The actuators are typically piston cylinder mechanisms aligned in the common plane of the rollers 4 and 6. The actuators are operated by air pressure along lines 12 and 14 from a control unit 16. As an alternative to piston cylinder mechanisms, lead screws may be used as actuators (8, 10) to set the spacing of the second roller 6 from the first roller 4. Lever mechanisms can also be used.

In order to monitor the tension in the belt 2, a sensor 18 in the form of a load cell or strain gauge is located behind the actuator 10. Suitable load cells are available from Procter & Chester Measurements Ltd. The sensor is subject to the same force as is delivered by actuator 10, and is therefore representative of the tension in the belt. The measurement taken can of course be used to estimate the tension at its opposite edge and thereby the variation across the width of the belt. Normally though, a separate sensor 22 would be located behind actuator 8 to monitor the force applied by the belt to the roller 6 at each edge of the belt.

A position sensor 20 monitors the lateral position of the belt relative to the rollers 4 and 6, and of course to the frame (not shown). The preferred sensor is an ultrasonic proximity sensor located above or below the belt edge and focussed on the edge. Suitable sensors are available from Hyde Park Sensors under the Trade Mark SUPERPROX. Various other types of sensors can also be used, such as optical (with a photocell), pneumatic (with an air jet), electrical (with a capacitative sensor) and mechanical (with a stylus). The sensor generates an electrical signal directly related to the lateral position of the belt edge, which signal is passed to the control unit 16.

In use, one of the rollers 4 and 6 is rotated by a motor to drive the belt 2 therearound. Figure 1 shows the upstream, movable roller 6 coupled to a motor 28 by a flexible coupling 30. The preferred lateral position of the belt, and the corresponding signal from the sensor 20 is entered into a computer at the control unit 16, which is programmed to monitor movements therefrom within a given range. Similarly the force applied by the belt to the roller 6 is monitored at sensors 18, 22 which also issue signals indicating the normal operating tension in the belt which is passed to the computer at the control unit 16. As and when the signals from the sensors 18, 20 and 22 indicate excessive lateral movement of the belt and/or excessive variation in the belt tension, then the computer instructs the control unit to operate the actuators 8, 10 to move the roller 6 to compensate for such variations. Thus, if an excessive lateral movement of the belt towards the actuator 10 is sensed, then the roller 6 would be tilted to guide the belt back to its preferred position. Whether the tilt is corrected by positive or negative operation of the actuators 8, 10 is determined by the tension of the belt as recognised by the sensors 18, 22. The conveyor belt system shown in Figure 1 uses rollers 4 and 6 of the same diameter, typically 90 mm, and is suitable for the horizontal movement of product in sorting machines of the kind described in United States Patent No: 5 538 142. If it is used directly to discharge products to be sorted into free flight through a viewing station for optical sorting, then the belt speed will be typically in the range of 3-5 m/s. It will be appreciated that at these speeds lateral movements of the belt and changes in the belt tension can occur very rapidly, with a significant risk of belt damage. The system described, by responding swiftly to these variations, can significantly prolong the useful life of a belt. If used as the delivery conveyor in a sorting machine of the kind disclosed in United States Patent No: 6 056 127, then lower speeds, up to 1 m/s may be used. The potential for failure nevertheless, particularly in a short conveyor system, remains.

Figures 2A and 2B illustrate a conveyor belt system in which the belt 2 extends round rollers 24 and 26 having different diameters. The roller 24 with the smaller diameter will normally be at the forward end of the conveyor, to create a small nose which can facilitate the discharge of product from the belt. It is particularly suitable for use as an inclined conveyor in sorting apparatus of the kind described in United States Patent No: 6 056 127 which is used to deliver a product to a viewing zone for optical sorting. The smaller roller 24, which normally has a diameter no greater than 100 mm, usually no more than 50mm, and can have a diameter as small as around 25 mm, reduces the size of any shadow in the viewing zone and the radius of any debris spray. However, it will be appreciated that for the same belt speed a roller of smaller diameter must rotate that much faster, and as a consequence the tension of the belt as it goes around the roller is of considerable importance. This is of particular significance as for use as the inclined conveyor in the sorting apparatus of the '127 Patent where once again, belt speeds in the range of 3- 5 m/s are contemplated. In a system of the type illustrated the diameter of the larger roller 26 could be around 150 mm, and the diameter of the smaller roller 24 around 30 mm.

In other respects, the conveyor belt system of Figure 2 operates in the same way as that of Figure 1, with lateral alignment being monitored by position sensor 20, and belt tension by the load sensor 18. The control unit and the lines connecting the sensors and actuators thereto are not shown.

Claims

1. A conveyor belt system comprising a belt extending around two rollers spaced by a distance equal to or less than the width of the belt, wherein one of the rollers is movable relative to the other roller by means of two actuators, each operable to move an end of the movable roller relative to the other roller, the system including a position sensor for monitoring the lateral position of the belt; a load sensor for monitoring the tension in the belt; and a computer for operating the actuators in response to signals from the sensors to position the movable roller so as to maintain the tension in the belt in a desired range and the belt in a correct lateral position on the rollers.

2. A system according to Claim 1 wherein the ratio of the width of the belt to the roller spacing is at least 1.2.

3. A system according to Claim 2 wherein said ration is substantially 1.5.

4. A system according to any preceding claim wherein the position sensor is a proximity sensor focussing on an edge section of the belt between the rollers.

5. A system according to any preceding claim wherein the load sensor comprises a load cell or strain gauge monitoring the force applied by the belt to one of the rollers at least at one end thereof.

6. A system according to Claim 5 wherein the load sensor monitors the force applied by the belt to the movable roller at each end thereof.

7. A system according to Claim 6 wherein each load cell is coupled to one of the actuators to monitor directly the reactive force generated in the actuator to hold the movable roller against the belt tension.

8. A system according to any preceding Claim wherein the movable roller is of larger diameter than the other roller.

9. A system according to Claim 8 wherein the movable roller is disposed at the upstream end of the conveyor belt system.

10. A system according to Claim 8 or Claim 9 wherein the diameter of the other roller is no more than 50 mm.

11. A system according to any preceding claim including means for driving the belt at speeds of up to 5m/s.

12. A system according to any preceding claim wherein the movable roller is a crowned roller.