ABRADING APPARATUS

Abstract

An abrading apparatus (1) including a drum (2), a movable abrasive surface (4) about at least part of the circumferential surface of the drum (2) and a plurality of treatment chambers (5) mounted about the drum (2). Each treatment chamber (5) has upstream and downstream faces (53, 54), which describe an open side facing the drum (2), such that the abrasive surface (4) forms a wall of the chamber (5). The downstream face (53) of each chamber (5) is substantially aligned with a radial plane (R) of the drum (2).

Claims

1. An abrading apparatus comprising a drum, a movable abrasive surface about at least part of the circumferential surface of the drum and one or more treatment chambers mounted about the drum, each treatment chamber having upstream and downstream faces describing an open side facing the drum such that the abrasive surface forms a wall of the chamber, wherein the drum comprises a radial plane parallel to the downstream surface of the chamber and the distance between the radial plane and the downstream face is less than the distance between the radial plane and the upstream face.

2. An abrading apparatus according to claim 1, wherein the distance between the radial plane and the downstream face is less than ½ of the distance between the radial plane and the upstream face.

3. An abrading apparatus according to claim 1, wherein the downstream face is substantially aligned with the radial plane.

4. An abrading apparatus according to claim 1, wherein the downstream face is substantially perpendicular to a facing portion of the abrasive surface.

5. An abrading apparatus according to claim 1, wherein each treatment chamber comprises upstream and downstream opposed wall portions extending toward the abrasive surface and a third wall portion adjoining the upstream and downstream wall portions, the upstream wall portion comprising the upstream face and the downstream wall portion comprising the downstream face, the downstream wall being spaced from the abrasive surface to provide a gap therebetween.

6. An abrading apparatus according to claim 5, wherein the or each treatment chamber is elongate, extends parallel to the axis of the drum and includes an inlet at a first end thereof, a primary outlet at a second end thereof and a secondary outlet provided by the gap.

7. An abrading apparatus according to claim 1, wherein each treatment chamber comprises an open channel section having an asymmetric cross-section.

8. An abrading apparatus according to claim 1 comprising a roller spaced from and substantially parallel to the drum, an endless abrasive loop mounted on the drum and roller and drive mechanism operable to rotate the drum and roller.

9. An abrading apparatus according to claim 8 comprising a tracking mechanism for adjusting automatically the axial position of the abrasive loop relative to the drum and roller, wherein the tracking mechanism comprises an analogue sensor for determining the position of the abrasive loop.

10. An abrading apparatus according to claim 8 comprising an enclosure within which is received the drum, the roller, the endless abrasive loop and the treatment chamber(s), wherein the enclosure comprises an isolation chamber which houses at least part of the roller and inhibits, in use, air entrained with the abrasive loop from entering the isolation chamber.

11. An abrading apparatus according to claim 1 comprising controller and sensor, wherein the controller is configured to vary, in use, automatically one or more control parameters of the apparatus in response to one or more process variables sensed by the sensor.

12. An abrading apparatus according to claim 11, wherein the sensor comprises a moisture sensor for measuring the moisture of objects to be treated by the treatment chambers or a pressure sensor for measuring the pressure in the treatment chamber(s) or an ammeter for measuring the current draw of the drive motor or a weight sensor for measuring the quantity of objects loaded into or processed by the apparatus.

13. An abrading apparatus according to claim 11, wherein the one or more control parameters comprises the speed of the motor.

14. A portable mill comprising an abrading apparatus according to claim 1, a power supply for powering the abrading apparatus and controller for controlling one or more control parameters of the abrading apparatus or of the power supply, the controller comprising wireless telecommunicator for communicating with a remote server, wherein the controller is configured to control at least one control parameter of the abrading apparatus and/or of the power supply in response to a command received, in use, by a remote server.

15. An abrading system comprising a remote server and one or more portable mills according to claim 14.

16. An abrading apparatus comprising: a drum; a roller spaced from and substantially parallel to the drum; an endless abrasive loop mounted over the drum and roller; one or more treatment chambers mounted about the drum; and a tracking mechanism for adjusting automatically the axial position of the abrasive loop relative to the drum and roller; wherein the tracking mechanism comprises an analogue sensor for determining the axial position of the abrasive loop.

17. A portable mill comprising an abrading apparatus according to claim 16, a power supply for powering the abrading apparatus and controller for controlling one or more control parameters of the abrading apparatus or of the power supply, the controller comprising wireless telecommunicator for communicating with a remote server, wherein the controller is configured to control at least one control parameter of the abrading apparatus and/or of the power supply in response to a command received, in use, by a remote server.

18. An abrading system comprising a remote server and one or more portable mills according to claim 17.

19. An abrading apparatus comprising: an enclosure within which is received: a drum; a tension roller spaced from and substantially parallel to the drum; an endless abrasive loop or belt mounted over the drum and tension roller; and one or more treatment chambers mounted about the drum; wherein the enclosure comprises an isolation chamber which houses at least part of the tension roller and inhibits, in use, abraded material from being captivated between the roller and the abrasive loop.

20. A portable mill comprising an abrading apparatus according to claim 19, a power supply for powering the abrading apparatus and controller for controlling one or more control parameters of the abrading apparatus or of the power supply, the controller comprising wireless telecommunicator for communicating with a remote server, wherein the controller is configured to control at least one control parameter of the abrading apparatus and/or of the power supply in response to a command received, in use, by a remote server.

Description

[0083] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0084] FIG. 1 is a partial side elevation of an abrading apparatus according to a first example showing two of its chambers;

[0085] FIG. 2 is a schematic top view of the abrading apparatus illustrating the layout of the drum, tail roller, abrasive belt and treatment chambers about part of the drum;

[0086] FIG. 3 is a partial section view illustrating a chamber and its position relative to the abrasive belt as compared with a prior art arrangement;

[0087] FIG. 4 is a partial section view similar to FIG. 3, but illustrating an alternative chamber design;

[0088] FIG. 5 is a schematic top view of an abrading apparatus according to a second example;

[0089] FIG. 6 is a schematic side view of the abrading apparatus of FIG. 5;

[0090] FIG. 7 is a schematic representation of the abrasive belt position sensing assembly of the apparatus of FIG. 5;

[0091] FIG. 8 is a chart illustrating the light intensity as a function of the belt position as measured by the belt position sensing assembly of FIG. 7 when using a photoresistor as the light sensor;

[0092] FIG. 9 is a chart illustrating the light intensity as a function of the belt position as measured by the belt position sensing assembly of FIG. 7 when using a photodiode as the light sensor; and

[0093] FIG. 10 is a schematic representation of a milling system incorporating the abrasion apparatus according to the second example.

[0094] Referring now to FIGS. 1 to 3, there is shown an abrading apparatus 1 including an enclosure 10 within which is received a drum 2, a tension or tail roller 3 spaced from and substantially parallel to the drum 2, an endless abrasive loop or belt 4 mounted over the drum 2 and tail roller 3, eight treatment chambers 5 mounted about the drum 2 and a control unit 6 mounted externally of the enclosure 10. A loading hopper 20 is located above the apparatus 1, which includes feed pipes 21 connected thereto and two moisture sensors 60, 61. Each feed pipe 21 is connected to the loading hopper 20, extends through a respective hole (not shown) in the enclosure 10 and feeds a respective one of the treatment chambers 5. A first moisture sensor 60 is in an upper portion of the hopper 20 for measuring the moisture content of objects as they are loaded into the hopper 20, the while second moisture sensor 61 is adjacent the base of the hopper 20 for measuring the moisture content of objects about to enter the treatment chambers 5. The moisture sensors 60, 61 are operatively connected to the control unit 6 and data measured by the moisture sensors 60, 61 is received by the control unit 6 for processing.

[0095] The enclosure 10, shown schematically in FIGS. 1 and 2, includes a frame with side panels 11 and a top panel 12. The drum 2 is substantially cylindrical, is rotatably mounted to the frame of the enclosure 10 in a vertical orientation and is rotationally driven about its axis X by a drive motor D in direction A. Drive motor D is an electric motor in this example. The tail roller 3 is also substantially cylindrical, but with a smaller diameter than the drum 2, and is also rotatably mounted to the frame of the enclosure 10 in an orientation that is substantially parallel to the drum 2.

[0096] The abrasive belt 4 includes a coating of sand or grit on a backing of cloth, paper or plastics, the particles being held in place by a resin or like bond. The abrasive belt 4 is mounted over the drum 2 and tail roller 3 and is held in tension therebetween such that rotation of the drum 2 causes the abrasive belt 4 to drive the tail roller 3 to rotate. It will be appreciated that the drive motor D may be coupled to the tail roller 3 instead of the drum 2 in some examples.

[0097] The treatment chambers 5 are equidistantly spaced about the circumferential portion of the drum 2 that is covered by the abrasive belt 4. Each treatment chamber 5 extends generally parallel to the axis X of the drum 2 and includes an elongate, open channel section mounted with its open side facing the drum 2 such that the abrasive belt 4 forms a wall of the treatment chamber 5. Each treatment chamber 5 includes an inlet 50 at its upper end, a primary outlet 51 at its lower end and a secondary outlet 52 along its length.

[0098] Each treatment chamber 5 also includes a first, upstream wall 53, a second, downstream wall 54 and a third, intermediate wall 55 perpendicular to, and joining, the first and second walls 53, 54 to describe a base of the treatment chamber 5, opposite the abrasive belt 4. The upstream wall 53 includes an inner, upstream face 53a and the downstream wall 54 includes an inner, downstream face 54a. The open side of each treatment chamber 5 is described between the upstream and downstream faces 53a, 54a.

[0099] The upstream wall 53 terminates adjacent the abrasive belt 4, with minimal clearance simply to avoid contact with the abrasive surface. Contrastingly, the downstream wall 54 is spaced from the belt 4 to provide a gap G sufficient to allow abraded material to pass therethrough, in use, thereby providing the secondary outlet 52. An optional extension wall 56 is secured to the third wall 55 and extends from the second, downstream wall 55, is substantially perpendicular thereto and describes, with the downstream wall 55, abrasive belt 4 and an adjacent treatment chamber 5, a discharge area 57. A vacuum source (not shown) draws abraded material from the discharge area 57 to a storage container (not shown).

[0100] Each treatment chamber 5 also includes three pressure sensors 62, 63, 64 mounted to the third wall 55. A first pressure sensor 62 is mounted adjacent the inlet 50 for measuring the pressure in an inlet region of the treatment chamber 5. A second pressure sensor 63 is mounted between the inlet 50 and the primary outlet 51 for measuring the pressure in a middle region of the treatment chamber 5. The third pressure sensor 64 is mounted adjacent the primary outlet 51 for measuring the pressure in an outlet region of the treatment chamber 5. The pressure sensors 62, 63, 64 are operatively connected to the control unit 6 and data measured by the pressure sensors 62, 63, 64 is received by the control unit 6 for processing.

[0101] The third wall 55 in this example is pivotally connected at its top by a hinge H relative to the first and second walls 53, 54 and is operatively connected to an actuator 65 adjacent its lower end. The actuator 65 is operatively connected to the control unit 6 for receiving control signals therefrom. As such, the orientation of the third wall 55 may be adjusted to vary the depth of the treatment chamber 5 along its length. It has been observed that increasing the depth of the chamber results in an increase in pressure in that area. As explained in EP 2094389, the applied pressure required to remove subsequent layers of whitened rice, for example, increases as the rice whitens. This is due to the higher toughness of the core of the grain. Consequently, gradually increasing the pressure exerted on the grains as they travel through the treatment chamber 5 maintains a consistent rate of removal of surface material.

[0102] Moreover, the abrading apparatus 1 in this example also includes an adjustable slide gate mechanism 66 adjacent the primary outlet 51. This slide gate mechanism 66 is adjustable to increase or decrease the size of the primary outlet 51. The slide gate mechanism 66 is operatively connected to the control unit 6 for receiving control signals therefrom to adjust its position (e.g. via an actuator thereof). As outlined above, the pressure within the treatment chamber 5 is also dependent upon the size of the primary outlet 51, which throttles the flow of objects flowing through the treatment chamber 5. As such, adjustment of the size of the primary outlet 51 using the adjustable slide gate mechanism 66 provides another control of the back pressure within the treatment chamber.

[0103] In use, the drive motor D effects the rotation of drum 2 in direction A, while the objects to be abraded are loaded into the hopper 20 and fed via the feed pipes 21 to the inlet 50 of treatment chambers 5. As the drum 2 rotates, it abrades the objects adjacent to its abrasive surface to remove a portion of the surface material. The objects pass from the inlet 50 to the primary outlet 51 of each treatment chamber 5, the abraded material being urged through the gap G under the downstream wall 54 and directed by the extension wall 56 to the discharge area 57 and transferred to a storage container (not shown) under the force of gravity and/or suction.

[0104] The objects circulate within the treatment chamber 5 along a peripheral flow path P under the action of the abrasive belt 4. The primary outlet 51 is smaller than both the inlet 50 and cross-sectional area within the treatment chamber 5, so as to throttle the flow of objects, thereby creating a back pressure within the treatment chamber 5. This back pressure urges the flowing objects against the abrasive belt 4, thereby removing one or more outer layers of the objects.

[0105] The objects entrained with the abrasive belt 4 are forced against the downstream wall 54 before riding up the downstream wall 54 and flowing back toward the upstream wall 53 along the intermediate wall 55. As such, the downstream wall 54 functions as a milling wall 54. As explained above, the material removed passes under the downstream milling wall 54 through the gap G and into the discharge area 57, while the abraded objects leave the chamber through the primary outlet 51. The treated objects are thus collected separately from the material removed and, for example, are passed into collection bags (not shown).

[0106] As illustrated more clearly in FIGS. 2 and 3, the downstream milling wall 54 of each treatment chamber 5 and its inner milling face 54a are substantially aligned with a radial plane R of the drum 2. As a result, the downstream milling wall 54 and its inner milling face 54a are substantially perpendicular to the tangential flow direction of the impacting objects. This is in contrast to the arrangement described in EP 0755304, in which the chamber position is depicted in dotted lines by the reference numeral 5′ in FIG. 3. The milling wall 54′ of this chamber 5′ forms an acute angle with the abrasive belt 4, which is believed to cause the objects to be prone to becoming wedged briefly adjacent the gap G. This, it is believed, abrades the objects more aggressively, which increases the instances of broken objects and results in the chamber 5′ cocking slightly in the direction of the peripheral flow path P.

[0107] As such, by moving the downstream milling wall 54 of the treatment chamber 5 toward the radial plane R of the drum 2, it is believed that the objects move more readily along the peripheral flow path P. It has been observed that this repositioning of the treatment chambers 5 not only reduces the instances of broken objects, but it also reduces the energy consumption of the abrading apparatus 1, as compared to the chamber arrangement described in EP 0755304. Whilst moving the downstream milling wall 54 to be substantially aligned with the radial plane R has been found to yield the most marked improvement, significant improvements have been observed when the distance between the radial plane R and the downstream face 54a is less than ¼, ½ or even ¾ of the distance between the radial plane and the upstream face.

[0108] FIG. 4 illustrates a treatment chamber 105 according to another example, which is similar to the treatment chamber 5 described above, wherein like features are labelled with like references with the addition of a preceding ‘1’. The treatment chamber 105 according to this example differs in that it is shaped to shaped to approximate the peripheral flow path P of the objects. In particular, treatment chamber 105 is asymmetric, in contrast with the rectangular cross-section of the treatment chamber 5 described above.

[0109] In this example, the third wall 155 is joined to the first, upstream wall 153 by a first chamfer wall 155a and is joined to the second, downstream milling wall 154 by a second chamfer wall 155b. The first chamfer wall 155a is larger than the second chamfer wall 155b, thereby providing an asymmetric cross-section along the treatment chamber 105. It will be appreciated by those skilled in the art that, in some examples, the third wall 155 may be at least partially curved, for example to provide a treatment chamber having a part-elliptical, part-obround or part-ovoid cross-section.

[0110] This treatment chamber 105 is similar to the treatment chamber disclosed in EP 2094389, but as with the treatment chamber 5 in the example above, it is displaced so that the downstream milling wall 154 is substantially aligned with the radial plane R of the drum 2. This chamber design therefore incorporates the benefits described in EP 2094389, wherein regions of flow stagnation are minimised. This inhibits objects from passing from the inlet 50 to the outlet 51 untreated or under-treated, thereby improving the consistency of treatment. It will be appreciated

[0111] Another feature of the abrading apparatus 1 is the provision of closed loop control. More specifically, the apparatus 1 is configured to monitor a plurality of process variables and to control the operation of the machine according to the monitored process variables. In this example, the process variables include moisture measured by the moisture sensors 60, 61, pressure measured by the pressure sensors 62, 63, 64 and current draw of the drive motor D measured by an ammeter (not shown) operatively connected thereto. The control parameters in this example include the rotational speed of the drive motor D, the depth variation of the treatment chamber 5 (controlled by the actuator 65 which changes the orientation of the third wall 55) and the size of the primary outlet 51 (controlled by the slide gate mechanism 66).

[0112] In use, the control unit 6 monitors the process variables and controls automatically the control parameters in response thereto. For example, if the moisture measured by the first moisture sensor 60 is less than that measured by the second moisture sensor 61, this suggests that the grains in the upper portion of the hopper 20 are drier than those in the lower portion of the hopper 20 and will therefore require higher processing pressures. When the moisture measured by the second moisture sensor 61 drops to correspond to this, lower value, the control unit 6 may control, after an appropriate delay, the slide gate mechanism 66 to change the size of the primary outlet 51 and/or the actuator 65 to change the orientation of the third wall 55 to alter the depth variation of the treatment chamber 5.

[0113] This, in turn, increases the back pressure within the treatment chamber 5 to maintain a substantially constant treatment of the grains. The pressure measured by the pressure sensors 62, 63, 64 and/or the current draw of the drive motor D measured by the ammeter (not shown) may be used by the control unit 6 to determine the effectiveness of the adjustment. It is also envisaged that the control unit 6 may include reference tables containing appropriate reference pressures and/or current draw values for particular moisture contents. In such cases, the measured values may be cross-referenced with those in the reference tables and adjustments made accordingly.

[0114] In addition, if a shift is detected in the pressure measured by the pressure sensors 62, 63, 64 and/or the current draw of the drive motor D measured by the ammeter (not shown), this may be indicative of a damaged or slipping abrasive belt 4 or of a change in the type of grain being processed. The control unit 6 may be configured to take one of a series of predetermined actions in response to the detected shift. For example, if the detected shift suggests that the abrasive belt 4 is damaged or slipping (e.g. if both the pressure and current draw decrease despite a constant rotational speed of the drive motor), the control unit 6 may stop the apparatus 1 and alert an operator or central control system (not shown) to the fault. Similarly, if the detected shift suggests that there has been an unexpected change in the type of grain being processed (e.g. if both the pressure and current draw increase despite a constant rotational speed and moisture readings), the control unit 6 may also stop the apparatus 1 and alert an operator or central control system (not shown).

[0115] In another example, the control unit 6 may be configured to receive an input, either automatically from a feed system (not shown) or manually from an operator (not shown), corresponding to a new grain type loaded into the hopper 20. In such a case, if the detected shift suggests a change in the type of grain being processed corresponding to the expected grain, the control unit 6 may alter automatically the appropriate control parameters. The aforementioned reference tables may include anticipated changes in process variables to identify the new type of grain being processed and/or the appropriate control parameters to be applied for the new grain type.

[0116] Turning now to FIGS. 5 to 7, there is shown an abrading apparatus 201 according to another example, which is similar to the abrading apparatus 1 described above, wherein like features are labelled with like references with the addition of a preceding ‘2’. The abrading apparatus 201 according to this example differs in that the enclosure 210 includes a primary chamber 213 and an isolation chamber 214 and the apparatus 201 includes a tracking system 207 and three suction assemblies 280, 281, 282.

[0117] The primary chamber 213 of the enclosure 210 according to this example is substantially cuboidal, surrounds the drum 202 and chambers 205 and includes an access door D. One of the side walls 211 of the primary chamber 213 extends between the drum 202 and the tail roller 203 and includes an opening through which the endless abrasive belt 204 extends between the drum 202 and tail roller 203. The isolation chamber 214 extends from this opening and encloses the tail roller 203, together with part of the endless abrasive belt 204 which extends between the drum 202 and tail roller 203.

[0118] In this example, the isolation chamber 214 approximates the shape of the tail roller 203 and the enclosed part of the endless abrasive belt 204. As such, the isolation chamber 214 is of a substantially prism-shape with a rounded apex. The isolation chamber 214 includes a transparent or translucent window 215 on each of its sides to enable the abrasive belt 204 to be viewed therethrough. The windows 215 are formed of a sheet of transparent or translucent acrylic in this example.

[0119] The isolation chamber 214 also includes a screen 216 extending from the interface joining the primary chamber 213 and the isolation chamber 214. The screen 216 terminates adjacent the abrasive belt 204 for inhibiting air entrained with the abrasive belt 204 from entering the isolation chamber 214. In this example, the screen 216 is a solid wall of sheet metal, but it may be replaced with a flexible sheet or brush element.

[0120] The purpose of the isolation chamber 214 is to inhibit abraded material from entering the vicinity of the tail roller 203, thereby reducing energy consumption and extends the useful life of the abrasive belt 204. As explained above, it is believed that air entrained with the abrasive belt 204 includes by-products of the treated small objects, which can be released into the air within the enclosure and become trapped between the tail roller 203 and abrasive belt 204, forced into the rear side of the belt 204 and become wedged between the drum 202 and the belt 204. This is believed to cause the abrasive belt 204 to stand proud of the drum 202 and urge it toward the treatment chambers 205, thereby causing variations in treatment characteristics and damaging the abrasive belt 204 prematurely.

[0121] A first suction assembly 280 includes a vacuum pipe 280a, a vacuum pump 280b and a storage bag 280c. The vacuum pipe 280a is fluidly connected to a base of the isolation chamber 214 adjacent the apex thereof. The vacuum pump 280b is configured to evacuate air containing abraded material from the isolation chamber 214. This reduces the amount of the aforementioned by-products in the isolation chamber 214, thereby inhibiting them from becoming trapped between the tail roller 203 and the abrasive belt 204. The abraded material and by-products so evacuated are captured within the storage bag 280c.

[0122] A second suction assembly 281 includes a vacuum pipe 281a, a vacuum pump 281b, a storage bag 281c and an isolation plate 281d. The isolation plate 281d is mounted to the frame of the enclosure 210 and extends from the last treatment chamber 205. The isolation plate 281d is mounted adjacent the abrasive belt 204 to describe a plenum therebetween to which the vacuum pipe 281a of the second suction assembly 281 is fluidly connected. The vacuum pump 281b is configured to evacuate air containing abraded material from the plenum described between the isolation plate 281d and the abrasive belt 204. This reduces the quantity of by-products on the abrasive belt 204 and/or entrained therewith prior to its entry into the isolation chamber 214. The abraded material and by-products so evacuated are captured within the storage bag 281c.

[0123] The third suction assembly 282 also includes a vacuum pipe 282a, a vacuum pump (not shown) and a storage bag 282c. The vacuum pipe 281a is fluidly connected to the discharge areas 57 (not shown in FIGS. 5 to 7) described between each of the isolation chambers 205. The vacuum pump (not shown) is configured to evacuate air containing abraded material from the discharge areas, which is then captured within the storage bag 282c.

[0124] The tail roller 203 is pivotally connected to the enclosure 210 at its upper end and the tracking system 207 includes an actuator 270 operatively connected to a lower end of the tail roller 203 for adjusting its orientation relative to that of the drum 202. The tail roller 203 is preferably rotatably mounted to a cradle (not shown), which itself is pivotally mounted relative to the drum 202 at or adjacent its uppermost end. This enables the actuator 270 to be operatively connected to the cradle at any position along its length. The actuator 270 is operatively connected to the control unit 206 for receiving commands therefrom to adjust the orientation of the tail roller 203 relative to the drum 202.

[0125] The tracking system 207 also includes a belt sensing assembly 271 mounted to the frame of the enclosure 210 adjacent an upper edge of the abrasive belt 204. The belt sensing assembly 271 is operatively connected to the control unit 206 and configured to determine the position of the abrasive belt 204. The movement of the abrasive belt 204 along the drum 202 and tail roller 203 is monitored by the control unit 206, which is configured to adjust the orientation of the tail roller 203 automatically, thereby to track the abrasive belt 204 up or down to maintain its position within a predetermined operating range. As will be appreciated by the skilled person, changing the orientation of the tail roller 203 will generate a different tension in the abrasive belt 204 toward one end of the tail roller 203 as compared with the tension at the other end. This tension differential creates an axial force on the abrasive belt 204, which causes it to move axially along the tail roller 203 and drum 202.

[0126] The belt sensing assembly 271, shown more clearly in FIG. 7, includes an analogue sensing means 272 for determining its axial position of the abrasive belt 204 on the drum 202 and tail roller 203. This is in contrast to the use of multiple separate sensors, which provide individual digital signals when certain threshold positions are detected. The use of an analogue sensing means 272 has been found to be surprisingly effective at optimising the operation of the abrading apparatus 201. More specifically, the control unit 206 is able to constantly and gradually adjust the orientation of the tail roller 203 on the basis of the analogue signal measured by the analogue sensing means 272. This has been found to prolong the life of the abrasive belt 204. Without wishing to be bound by any theory, this is believed to be the result of less aggressive forces being applied to the abrasive belt 204 during such adjustment.

[0127] In this example, the analogue sensing means 272 is only adjacent the upper edge of the abrasive belt 204, but it may also be advantageous to include such a sensing means 272 adjacent its lower edge. The analogue sensing means 272 includes a transmitter 273 and a sensor or receiver 274. The transmitter 273 is received in a transmitter housing 275 on a first side of the abrasive belt 204, while the sensor 274 is received in a sensor housing 276 on a second side of the abrasive belt 204. The housings 275, 276 each include an elongate slot or window 277, 278 which faces the abrasive belt 204, with its longitudinal dimension perpendicular to the upper edge of the abrasive belt 204. In this example, each window 277, 278 is 10 mm in length.

[0128] The transmitter 273 is operable to transmit an analogue signal S through the window 277 in the transmitter housing 275, through the window 278 in the sensor housing 276 and toward the sensor 274. The sensor 274 is operable to detect or measure the analogue signal S transmitted by the transmitter 273. However, the abrasive belt 204 masks part of the signal S as it passes between the facing windows 277, 278. As such, the magnitude of the signal S detected or measured by the sensor 274 is a function of the position of the abrasive belt 204. More specifically, the higher the abrasive belt 204, the weaker the signal S received by the sensor 274.

[0129] In this example, the transmitter 273 is a light transmitter or a light source operable to emit visible light, preferably white light. The transmitter 273 preferably includes one or more light emitting diodes (LEDs) that are operable to emit at least 200 lumens, such as 300 lumens or more. The sensor 274 is a light sensor, specifically a photoelectric device or a photo sensor. The light sensor 274 can be a photoresistor or light dependent resistor, in which case it may have a major dimension of 10 mm to ensure that it receives all light which passes through the window 278. Alternatively, the light sensor 274 can be a photodiode.

[0130] As the abrasive belt 204 moves up and down relative to the belt sensing assembly 271, the extent to which the light emitted by the transmitter 273 is masked by the abrasive belt 204 varies. This changes the intensity of light detected or measured by the sensor 274, thereby providing a reading that is indicative of the position of the belt. This reading is then used by the control unit 206 to control the tracking system 207, as outlined above, to maintain the abrasive belt 204 in the desired position range.

[0131] FIG. 8 illustrates the relationship between the light intensity detected by the light sensor 274 and the actual measured position of the abrasive belt 204, where the light sensor 274 is a photoresistor. FIG. 9 illustrates the same relationship, but using a light sensor 274 that is a photodiode. As illustrated by these Figures, the change in light intensity detected by the light sensor 274 is more acute when the edge of the abrasive belt 204 is adjacent the centre of the slot when the light sensor 274 is a photoresistor, whilst the relationship is relatively linear across the entire range of movement of the abrasive belt 204 in the case of the photodiode. The photodiode may be favoured in certain examples because of this, linear relationship. However, adjustment of the orientation of the tail roller 203 may be carried out using a control algorithm that favours the relationship provided by the photoresistor in certain examples.

[0132] Turning now to FIG. 10, there is shown a milling system 9 including a remote server 90 and a portable mill 91. The portable mill 91 includes a shipping container 92 within which is received an abrading apparatus 201 as described above, together with an energy storage device 93, a diesel generator 94, a discharge conveyor 95, a vision system 96, a storage container 97 for treated objects and a waste container 98 for rejected objects. The portable mill 91 also includes solar panels 99 mounted to a roof 92a of the shipping container 92. The energy storage device 93, diesel generator 94, discharge conveyor 95 and vision system 96 are all operatively connected to, and controlled by, the control unit 206 of the abrading apparatus 201.

[0133] The abrading apparatus 201 includes moisture sensors 260, 261 and pressure sensors (not shown) similar to those described above in relation to the first example. Each suction assembly 280, 281, 282 includes a weight sensor 265, 266 (only two of which are shown in FIG. 10) for weighing the abraded material contained in their respective storage bags 280c, 281c, 282c. Similarly, weight sensors 267, 268, 269 are also included in each of the hopper 220, the storage container 97 and waste container 98. In addition, the control unit 206 includes a wireless telecommunications device 206a for communicating with a corresponding wireless telecommunications device 90a of the remote server 90.

[0134] The energy storage device 93 is electrically connected to the abrading apparatus 201 by a cable 93a for supplying power thereto. The diesel generator 94 and solar panels 99 are both electrically connected to the energy storage device 93 by respective cables 94a, 99a and supply generated thereto for storage and subsequent supply to the abrading apparatus 201. The discharge conveyor 95 is a split conveyor assembly which includes a first, inclined conveyor 95a that receives abraded objects from the treatment chambers 205 and a second, feed conveyor 95b with a first, inlet end above the waste container 98 and below but offset from the first conveyor 95a and a second, outlet end above the storage container 97. The discharge conveyor 95 also includes a reject flap 95c between the first and second conveyors 95a, 95b. The reject flap 95c is pivotable between a first position (shown in FIG. 10), in which it directs abraded objects from the first conveyor 95a onto the second conveyor 95b, and a second position, in which abraded objects from the first conveyor 95a are directed into the waste container 98.

[0135] In this example, the vision system 96 includes a camera 96a and a wireless transmitter 96b for transmitting captured image data to the control unit 206. The camera 96a is located adjacent an upper end of the first conveyor 95a for capturing image data of abraded objects conveyed therealong. The image data captured by the vision system 96 is processed, either locally by the vision system 96 or by the control unit 206, to compare the image data to a reference image, outline or model to identify treated objects that should be classified as damaged or broken. The vision system 96 or control unit 206 then determines a value indicative of the quantity or proportion of damaged or broken objects treated by the abrading apparatus 201 based on the identification.

[0136] In this example, the control unit 206 is configured to operate the reject flap 95c to direct abraded objects into the waste container 98 when the determined value is above a predetermined threshold.

[0137] In addition, the calculated value determined from the image data captured by the vision system 96 can also be used by the control unit 206 as a process variable for controlling the operation of the abrading apparatus 201, as described above in relation to the abrading apparatus 1 according to the first example. Similarly, the control unit 206 may process the values measured by the weight sensors 265, 266, 267, 268, 269 to determine the quantity of abraded material generated over a predetermined period of time, the quantity of objects loaded into the hopper 220, the quantity of treated objects and the quantity of damaged or broken objects. These values may be used as further process variables in the closed loop control algorithms outlined above. More specifically, some or all of the current draw of the motor (from the ammeter), rotational speed of the motor, moisture levels (from moisture sensors 260, 261), chamber pressures (from the pressure sensors), image data (obtained from the vision system 96), the quantity of abraded material (from weight sensors 265, 266), the quantity of material loaded in the hopper (from weight sensor 267), the quantity of treated objects (from weight sensor 268) and/or the quantity of damaged or broken objects (from weight sensors 269) may be used by the control unit 206 to monitor and/or control the operation of the apparatus 201.

[0138] One or more aspects of the operation of the portable mill 91 may be monitored and/or controlled by the remote server 90. For example, the control unit 206 may be configured to send to the remote server 90, via the wireless telecommunications devices 206a, 90a, data relating to one or more of the aforementioned process variables and/or relating to one or more control parameters. The remote server 90 may be configured to send to the control unit 206, via the wireless telecommunications devices 90a, 206a, one or more commands relating to one or more control parameters. One or more of the control features described above in relation to the control unit 6, 206 may be incorporated in or carried out by the remote server 90. Alternatively, the remote server 90 may simply be configured to enable or disable one or more features of the portable mill 91, such as the power supplied to the abrading apparatus 201.

[0139] The remote server 90 may also include a costing module or algorithm configured to calculate a cost associated with one or more of the operating and/or control parameters and/or an operating period. For example, the costing module may be configured to calculate a cost based on a period of operation. Alternatively, the costing module may be configured to calculate a cost based on a weight of objects loaded in the hopper 220 and/or a weight of treated objects and/or a weight of damaged or broken objects and/or a weight of abraded material. The control unit 206 may be configured to monitor a change in such weights over time, as detected by the weight sensors 265, 266, 267, 268, 269 and/or may include one or more redundant sensors for ensuring the accuracy of the quantity of objects treated.

[0140] The remote server 90 may include a customer database, which may include one or more customer details (e.g. one or more of a contact name, address, telephone number, account number, credit limit, rating or history, payment terms and the like). The remote server 90 may include an invoicing module or algorithm configured to generate an invoice based on one or more costs calculated by the costing module or algorithm.

[0141] The control unit 206 may include an input means (not shown) for capturing data relating to a customer or payment means (e.g. credit card). The control unit 206 may be configured to send to the remote server 90, via the wireless telecommunications devices 206a, 90a, data relating to the customer or payment means.

[0142] The remote server may comprise a payment module or algorithm configured to associate an invoice generated by the invoicing module or algorithm with a customer or payment means. The payment module or algorithm may be configured to retrieve a payment from the payment means or a payment means associated with a customer. The retrieved payment may correspond to an invoice generated by the invoicing module.

[0143] Other features associated with automatic payment means will be appreciated by those skilled in the art.

[0144] It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. For example, the abrading apparatus 1, 201 need not include all of the features described herein. In addition, the abrading apparatus 1, 201 may include one or more further features, such as a further vision system configured to capture image data relating to the abraded material. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.