Technical Field of Invention

The present invention relates to a contact cleaning apparatus. In particular, though not exclusively, the invention relates to a contact cleaning apparatus comprising a contact cleaning carriage with a height adjustable contact cleaning surface.

Background

Contact cleaning is used to clean a substrate surface or work piece. Once cleaned, the work piece may be used in a variety of sophisticated processes such as in the manufacturing of electronics, photovoltaics and flat panel displays. Usually, a rubber or elastomeric contact cleaning roller is used to remove contaminating particles from a work piece, and an adhesive roll can then be used to remove the contaminating particles or debris from the cleaning roller. This ensures the cleaning roller remains free from debris and allows the cleaning roller to maximise its efficiency in removing contaminating particles from the substrate surface or work piece.

The cleaning roller typically includes a shaft or core with an elastomeric coating applied to its outer surface. The elastomer is then cured on the core so that its outer surface forms the cleaning surface. Optionally, the cleaning surface may be microscopically roughened to increase and/or maximise surface area contact between the cleaning surface and the small particles causing the contamination.

Production of advanced electronics increasingly requires no defects due to miniaturisation, increased process measurement and customer compliance. Cleaning of electronic components, for example printed circuit boards (PCBs), is required to remove particles and other contamination.

Cleaning components which are static sensitive, or which are prone to becoming statically charged is challenging.

Low static elastomeric cleaning rollers can be used to reduce static charging in the work pieces during cleaning. The elastomeric rollers are located above a conveyor, which conveys the work piece to be cleaned to the contact cleaning roller. The work piece then pushes the roller upwards against springs, such that a force is constantly applied to the work piece from the contact cleaning roller. The thicker the work piece, the greater the force applied by the contact cleaning roller. The increased force increases the risk of static charging of the work piece and damage to the work piece. In addition, the contact between the work piece and the contact cleaning roller causing the contact cleaning roller to move to accommodate the thickness of the work piece as it passes through the apparatus can, eventually, cause damage to the surface of the contact cleaning roller, typically an elastomer. It is known to adjust the height of the rollers by manual intervention, such as via a stand-off screw. It is also known to accommodate varying work piece thickness by having, for example, four set height positions for the contact cleaning roller above the conveyor.

It is an object of the invention to mitigate the drawbacks of the known contact cleaning apparatus.

Summary of the Invention

In accordance with the present invention there is provided a contact cleaning apparatus according to the appended claims.

In accordance with the present invention there is provided a method of cleaning a work piece.

According to an aspect of the present invention there is provided a contact cleaning apparatus for cleaning a work piece, the contact cleaning apparatus comprising an inlet for introducing the work piece into the contact cleaning apparatus and an outlet for removing the work piece from the contact cleaning apparatus; a contact cleaning carriage with a contact cleaning surface attached thereto, the contact cleaning carriage being located between the inlet and the outlet; a conveyor for conveying the work piece from the inlet to the outlet and between the contact cleaning surface and the conveyor; a carriage sensor for measuring a distance between the conveyor and the contact cleaning carriage; at least one cam operably connected to the contact cleaning carriage; wherein the at least one cam is rotatable to move the contact cleaning carriage in a direction normal to the conveyor to control the distance between the contact cleaning carriage and the conveyor.

By controlling the distance between the conveyor and the contact cleaning carriage, the distance between the contact cleaning surface attached to the contact cleaning carriage and the conveyor is also controlled. In certain embodiments, the contact cleaning apparatus comprises a controller (e.g. a processor) operably coupled to the carriage sensor and the at least one cam. More specifically, the controller (e.g. a processor) is programmable with a predetermined target distance between the conveyor and the contact cleaning carriage. In this way, a user is able to programme a predetermined target distance into the controller (e.g. a processor) which is equivalent to or proportional to the thickness of the work piece to be cleaned. In certain embodiments, the controller is operable to adjust the height of the contact cleaning carriage above the conveyor to the predetermined target distance. In use, the controller maintains the contact cleaning carriage at the predetermined target distance above the conveyor by operating the at least one cam.

In certain embodiments the predetermined target distance is calculated by the controller (e.g. a processor) from a sum of a work piece thickness (input by a user) and an adjustment factor. More specifically, the adjustment factor reduces the work piece thickness to provide the predetermined target distance. Yet more specifically, the adjustment factor may be up to 0.25mm. In these embodiments, the predetermined target distance is slightly less than the work piece thickness input into the controller (e.g. a processor) by the user. In this way, the contact cleaning surface is always able to contact the surface of the work piece on the conveyor. Furthermore, by applying an adjustment factor to reduce the work piece thickness input by the user, the strain rate (i.e. the load) applied to the work piece by the contact cleaning surface is controlled so as not to damage the work piece. In use, the distance between the contact cleaning carriage and the conveyor is maintained as constant until the user inputs a new work piece thickness into the controller and a new predetermined target distance is calculated by the controller.

In certain embodiments, the carriage sensor is operable to monitor the distance between the conveyor and the contact cleaning carriage.

In certain embodiments, the carriage sensor is operable to continuously monitor the distance between the conveyor and the contact cleaning carriage.

In certain embodiments, the carriage sensor is operably linked to an alarm. More specifically, the carriage sensor is operable to detect the distance between the conveyor and the contact cleaning carriage and to feedback the distance to the controller (e.g. a processor). The controller (e.g. a processor) is operable to compare the predetermined target distance to the distance detected by the carriage sensor. If the distance detected by the carriage sensor and the predetermined target distance do not match, the controller (e.g. a processor) is configured to activate an alarm. In this way, if the work piece is of a greater thickness dimension than the predetermined target distance, the contact cleaning carriage will be pushed upwards and the distance between the conveyor and the contact cleaning carriage detected by the carriage sensor will increase so as not to match the predetermined target distance.

It is advantageous to provide a contact cleaning carriage which is moveable in a direction normal to the conveyor. Thus, by operating the at least one cam, the distance between the conveyor and the contact cleaning carriage is adjustable.

It is advantageous to use rotating cam/s to adjust the height of the contact cleaning carriage which allows the distance between the conveyor and the contact cleaning carriage to be adjusted in response to the controller communicating the predetermined target distance to the cam/s.

In certain embodiments, the distance between the contact cleaning carriage and the conveyor is adjustable to control the strain rate (i.e. load applied) to the work piece by the contact cleaning surface.

In certain embodiments the contact cleaning apparatus further comprises at least one load sensor mounted to the contact cleaning carriage.

Alternatively, the contact cleaning apparatus further comprises at least one load sensor mounted to the at least one cam between the cam surface and the contact cleaning carriage.

In embodiments comprising more than one cam, the contact cleaning apparatus further comprises at least one load sensor from each cam, the load sensors each being mounted to the contact cleaning carriage.

Alternatively, in embodiments comprising more than one cam, the contact cleaning apparatus further comprises at least one load sensor mounted to each cam between the cam surface and the contact cleaning carriage. In this way, a balanced load can be detected and communicated to the controller (e.g. processor).

In certain embodiments, the load sensor is a load sensing resistor.

In certain embodiments, the at least one load sensor is configured and located to measure a load applied to the work piece by the contact cleaning surface.

In certain embodiments, the load sensor is located between the contact cleaning carriage and the cam surface. In certain embodiments, the load sensor is able to feedback load information to the controller (e.g. a processor).

The load sensor may provide an alert and/or suspend the operation of the contact cleaning apparatus, in the event that the load is outside of a predetermined range. In this way, the strain rate applied to the work piece by the contact cleaning surface is maintained within a predetermined range.

In certain embodiments, the controller (e.g. a processor) may be operable to adjust the position of the cam in response to the load information in order to maintain the load applied to the cam surface by the contact cleaning carriage within a predetermined range.

In certain embodiments, at least one electric motor (e.g. a stepper motor) is operably coupled to the at least one cam.

In certain embodiments, the controller (e.g. a processor) energises the at least one electric motor to rotate the at least one cam. In this way, the controller (e.g. a processor) is operable to adjust the height of the contact cleaning carriage above the conveyor to the predetermined distance.

It is advantageous to adjust the height of the contact cleaning surface above the conveyor by rotating a cam in response to an electric motor. By automating the height adjustment and monitoring in the contact cleaning apparatus, this also reduces the risk of human error in manually adjusting the height of the cleaning carriage above the conveyor, which manual intervention may cause damage to the work piece. This also reduces the time taken to adjust the height in response to a change in the thickness of subsequent work pieces.

In certain embodiments, the carriage sensor may be a proximity sensor (e.g. a hall effect sensor or a laser proximity sensor).

The use of a proximity sensor is advantageous as it is low cost whilst providing a rapid measurement.

In certain embodiments, the contact cleaning surface comprises at least one contact cleaning roller (e.g. an elastomeric roller). More specifically, the at least one contact cleaning roller may be rotationally mounted to the contact cleaning carriage. Yet, more specifically, the at least one contact cleaning roller may comprise two contact cleaning rollers. In certain embodiments, the at least one cam comprises two cams disposed on a common shaft. More specifically, the two cams may be located at either side of the contact cleaning carriage and are operably connected to the contact cleaning carriage such that the work piece is conveyed therebetween. Yet more specifically, the two cams may be located in the centre of the contact cleaning carriage, in the direction in which the work piece is conveyed. In this way, the cams act on the contact cleaning carriage rather than on the contact cleaning surface directly thus avoiding damage to the contact cleaning surface.

Locating the two cams in the centre of the contact cleaning carriage is advantageous as it prevents misalignment of the contact cleaning carriage as it moves in a direction perpendicular to the conveyor.

In certain embodiments, the at least one electric motor may be operably coupled to the common shaft.

In certain embodiments, the contact cleaning apparatus comprises an exit sensor located between the contact cleaning carriage and the outlet, for detecting a work piece having exited from between the contact cleaning surface and the conveyor. More specifically, the exit sensor may be a proximity sensor (e.g. a hall effect sensor or a laser proximity sensor).

In certain embodiments, the exit sensor is operably coupled to the controller (e.g. a processor). The controller (e.g. a processor) may be operable to cause a reset in the position of the cam in response to the exit sensor detecting a work piece. In this way, the contact cleaning surface may be reset in position ready for the next work piece to be detected by the carriage sensor.

In certain embodiments, the carriage sensor is mounted to the contact cleaning carriage.

In certain embodiments, in the absence of a work piece between the contact cleaning surface and the conveyor, the carriage sensor is operable to measure the distance to the conveyor and provide a datum measurement for the rotation of the at least one cam. The datum measurement may be obtained when the distance between the contact cleaning carriage and the conveyor is equal to the predetermined target distance.

In certain embodiments, the axis of rotation of the at least one cam may be fixed relative to the conveyor, and the contact cleaning carriage may be urged (e.g. via a spring or weight) into sliding contact with the circumferential surface of the at least one cam. In certain embodiments, the contact cleaning apparatus comprises an adhesive roll which is in tangential contact with the contact cleaning surface.

In certain embodiments, the projection profile of the work piece (i.e. the work piece to be cleaned) has a thickness of between 0.2 mm and 6 mm. In such embodiments, the programmed distance will be equal to between 0.2 mm and 6 mm. In embodiments wherein the adjustment factor is 0.25mm, for example, the predetermined target distance will be between 0.25mm less than the work piece thickness programmed into the controller.

In certain embodiments, the conveyor is a belt conveyor.

In certain embodiments, the conveyor is a roller conveyor.

In certain embodiments, the work piece is a printed circuit board with components mounted thereto.

According to an aspect of the invention, there is provided a surface-mount-technology machine comprise the contact cleaning apparatus as described herein.

According to another aspect of the invention, there is provided a method of cleaning a work piece, the method comprising the steps of introducing the work piece into a contact cleaning apparatus through an inlet; conveying the work piece on a conveyor towards a contact cleaning carriage which has a contact cleaning surface attached thereto; measuring a distance between the conveyor and the contact cleaning carriage using a carriage sensor; rotating at least one cam, which is operably connected to the contact cleaning carriage, to move the contact cleaning carriage in a direction normal to the conveyor to control the distance between the contact cleaning carriage and the conveyor; conveying the work piece between the contact cleaning surface and the conveyor; conveying the work piece towards an outlet for removal from the contact cleaning apparatus.

By controlling the distance between the conveyor and the contact cleaning carriage, the distance between the contact cleaning surface attached to the contact cleaning carriage and the conveyor is also controlled.

In certain embodiments, the method comprises the steps of providing a controller (e.g. a processor) operably coupled to the carriage sensor and the at least one cam; and programming the controller (e.g. a processor) with a predetermined target distance between the conveyor and the contact cleaning carriage. In these embodiments, the controller (e.g. a processor) is operable to rotate the at least one cam to move the contact cleaning carriage to the predetermined target distance above the conveyor.

In certain embodiments, the carriage sensor continuously monitors the distance between the conveyor and the contact cleaning carriage.

In certain embodiments, the controller (e.g. processor) activates an alarm when the distance between the conveyor and the contact cleaning carriage monitored by the carriage sensor does not match the predetermined target distance

It is advantageous to provide a contact cleaning carriage which is moveable in a direction normal to the conveyor. Thus, by operating the at least one cam, the distance between the conveyor and the contact cleaning carriage is adjustable.

In certain embodiments, the distance between the contact cleaning carriage and the conveyor is adjustable to control the strain rate (i.e. load applied) on the work piece by the contact cleaning surface.

In certain embodiments the strain rate (i.e. load applied) on the work piece by the contact cleaning surface is controlled in response to load information provided to the controller (e.g. processor) from at least one load sensor mounted between the contact cleaning carriage and the at least one cam.

In certain embodiments, rotation of the at least one cam is provided by energising at least one electric motor (e.g. a stepper motor) which is operably coupled to the at least one cam.

In certain embodiments, a controller (e.g. a processor) is operable to energise the at least one electric motor to rotate the at least one cam.

In certain embodiments, the method may further include the step of measuring the distance between the contact cleaning carriage and the conveyor and providing a datum measurement for the rotation of the at least one cam.

In certain embodiments, the datum measurement between the contact cleaning carriage and the conveyor is equal to the predetermined target distance. In certain embodiments, the method further comprises a step of detecting if the work piece has exited from between the contact cleaning surface and the conveyor using an exit sensor.

Brief Description of Drawings

Example embodiment(s) of the invention are illustrated in the accompanying drawings, in which:

Figure 1 illustrates a contact cleaning apparatus according to the invention;

Figure 2 illustrates a detailed view of the contact cleaning apparatus of Figure 1 ;

Figure 3 illustrates a top view of the contact cleaning apparatus of Figure 2, with the adhesive roll and the conveyor omitted;

Figure 4 illustrates the contact cleaning apparatus of Figure 1 in use;

Figure 5 illustrates the contact cleaning apparatus of Figure 1 in use;

Figure 6 illustrates the contact cleaning apparatus of Figure 1 in use;

Figure 7 illustrates the contact cleaning apparatus of Figure 1 in use; and

Figure 8 illustrates a contact cleaning apparatus according to a second embodiment of the invention.

Detailed Description

Certain terminology is used in the following description for convenience only and is not limiting. The words ‘upper’ and ‘lower’ designate directions in the drawings to which reference is made and are with respect to the described component when assembled, the particular meaning being readily apparent from the context of the description.

Further, as used herein, the terms ‘connected’, ‘attached’, ‘coupled’, ‘mounted’ are intended to include direct connections between two members without any other members interposed therebetween, as well as indirect connections between members in which one or more other members are interposed therebetween. The terminology includes the words specifically mentioned above, derivatives thereof, and words of similar import.

Further, unless otherwise specified, the use of ordinal adjectives, such as, ‘first’, ‘second’, ‘third’ etc. merely indicate that different instances of like objects are being referred to and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking or in any other manner.

The embodiments of the invention, as illustrated in Figures 1 -8, relate to contact cleaning apparatus. The contact cleaning apparatus are used to clean work pieces, for example, but not limited to, printed circuit boards (PCBs).

Referring first to Figure 1 , there is shown a contact cleaning apparatus 1 which comprises a contact cleaning carriage 2, for cleaning a work piece therein. The contact cleaning apparatus 1 has an inlet 11 for introducing the work piece to the cleaning apparatus 1 . The contact cleaning apparatus 1 has an outlet 12 for removing the work piece to be cleaned from the contact cleaning apparatus 1 . The work piece is transported from the inlet 11 to the contact cleaning carriage 2, and then to the outlet 12, by a conveyor 13. Movement of the conveyor 13 may be controlled by a controller (not shown), or may be set to a predetermined speed which is inputted to the controller.

Referring now to Figures 2 and 3, the contact cleaning apparatus 1 is shown in detail. The contact cleaning carriage 2 is located partway between the inlet 11 and the outlet

12. The contact cleaning carriage 2 has two contact cleaning rollers 21 . The contact cleaning rollers 21 are preferably elastomeric cleaning rollers. The contact cleaning rollers 21 are parallel to each other, parallel to the conveyor 13, and perpendicular to the direction of travel of the conveyor 13 (which is illustrated by the arrows in Figure 2).

The cleaning apparatus 1 comprises a carriage frame 22. The carriage frame 22 has two side portions, where one side portion is disposed at either end of the contact cleaning rollers 21. The contact cleaning rollers 21 are rotationally mounted to the side portions, such that the contact cleaning rollers 21 are of substantially equal distances from the conveyor 13. The two side portions are optionally interconnected by front and rear portions extending in a perpendicular direction to the direction of travel of the conveyor

13. The optional interconnecting portions are spaced from the contact cleaning rollers 21 on the inlet side and on the outlet side respectively. Located in tangential contact with both contact cleaning rollers 21 is an adhesive roll 23. The adhesive roll 23 is located such that the contact cleaning rollers 21 are located between the adhesive roll 23 and the conveyor 13. The adhesive roll 23 is of any kind known in the art. For example, the adhesive roll 23 may comprise a sheet of adhesive material which is unwound from the adhesive roll 23 as the adhesive roll 23 rotates.

The contact cleaning apparatus 1 comprises two circular cams 3. The carriage frame 22 rests upon the circumferential surfaces of the cams 3. The cams 3 are located approximately halfway between the inlet side and the outlet side of the carriage frame 22 and spaced from either end of the contact cleaning rollers 21 . The cams 3 are mounted to a cam shaft 31 , such that the cam shaft 31 is offset from the centre of the cams 3. The cam shaft 31 is operably coupled to an electric motor (not shown). The electric motor is preferably a stepper motor. The electric motor is in wired or wireless communication with the controller, and energisation of the electric motor to rotate the cam shaft 31 is controlled by the controller. Energisation of the electric motor causes the cam shaft 31 and cams 3 to rotate, causing the carriage frame 22, contact cleaning rollers 21 and adhesive roll 23 to move in a direction perpendicular to the conveyor 13. Guides (not shown) maintain the movement of the carriage frame 22 in a direction perpendicular to the conveyor 13. Locating the cams 3 approximately halfway between the inlet side and the outlet side of the carriage frame 22 is beneficial to maintaining alignment, as the carriage frame 22 moves along the guides. Each cam 3 comprises a maximum radius and a minimum radius. When the carriage frame 22 rests upon the minimum radii of the cams 3, the distance between the contact cleaning rollers 21 and the conveyor 13 is at a minimum, e.g. substantially zero, or 0.1 mm or 0.2 mm. When the carriage frame 22 rests upon the maximum radii of the cams 3 the distance between the contact cleaning rollers 21 and the conveyor 13 is at a maximum, e.g. approximately 5 mm, or 6 mm, or 7 mm. This enables cleaning of work pieces of between 0.2 mm and 6 mm, for example.

Contact between the carriage frame 22 and the cams 3 is maintained due to the weight of the carriage frame 22, contact cleaning rollers 21 and adhesive roll 23. A spring (not shown) may also be used to urge the carriage frame 22 towards the conveyor 13.

The contact cleaning apparatus 1 further comprises a carriage sensor 4. The carriage sensor 4 is a proximity sensor, such as a hall-effect sensor or a laser proximity sensor. The carriage sensor 4 measures the distance between the facing surfaces of the conveyor 13 and the carriage frame 22. The controller is in wired or wireless communication with the carriage sensor 4 and obtains the distance measured by the carriage sensor 4. The controller is a programmable processor into which a work piece thickness and adjustment factor are programmed. The controller calculates a predetermined target distance by subtracting the adjustment factor from the work piece thickness input by the user. The controller is operable to adjust the height of the carriage frame 22 above the conveyor 13 to the predetermined target distance by energising the electric stepper motor which in turn rotates the cams 3 until the carriage sensor 4 detected distance is equal to the predetermined target distance.

The carriage sensor 4 is located such that it is substantially level with the conveyor 13, such that the carriage sensor 4 measures the distance between the carriage frame 22 and the conveyor 13, in a direction perpendicular to the conveyor 13. The carriage sensor 4 is configured to continuously measure the distance between the carriage frame 22 and the conveyor 13, so that this distance can be monitored by the controller. Also, numerous carriage sensors 4 may be provided, for example, to account for misalignment in the carriage frame 22.

The contact cleaning apparatus 1 further comprises two load sensors 5, which are load sensing resistors. The load sensors 5 are mounted on either side of the carriage frame 22, and contact the surface of cams 3. The load sensors 5 provide a reading of a load applied by the carriage frame 22 on the cams 3 which is directly proportional to the load applied by the cleaning rollers 21 to a work piece. The load sensors 5 continuously measure the load applied by the carriage frame 22 onto the surface of the cams 3. Depending on the configuration of the cleaning apparatus 1 , the load sensors 5 may be in wired or wireless connection to the controller; and/or in wired or wireless connection with an alarm or alert system (not shown); and/or in wired or wireless communication with a shut-off system (not shown) for the contact cleaning apparatus 1 . Accordingly the contact cleaning apparatus 1 may be configured, in the event that the load sensors 5 measure a load which is outside of a predetermined tolerance, to increase or decrease the distance between the carriage frame 22 and the conveyor 13 to bring the load to within the tolerance; and/or to set of an alarm or an alert; and/or to suspend operation of the contact cleaning apparatus 1 .

The cleaning apparatus 1 further comprises an inlet sensor 6, located between the inlet 11 and the contact cleaning carriage 2. The inlet sensor 6 is an object-detection sensor. The inlet sensor 6 may be in wired or wireless communication with the controller; and/or in wired or wireless communication with a counter (not shown) and/or a status identifier.

The cleaning apparatus 1 further comprises an exit sensor 7, located between the contact cleaning carriage 2 and the outlet 12. The exit sensor 7 is an object-detection sensor. The exit sensor 7 may be in wired or wireless communication with the controller; and/or in wired or wireless communication with a counter (not shown) and/or a status identifier.

If the controller controls the conveyor 13 then the controller is in wired or wireless communication with the conveyor 13. Otherwise, the controller may be provided with the speed of movement of the conveyor.

Turning now to Figure 4-7, the cleaning of a work piece A is described.

Firstly, the thickness of the work piece A is provided to the controller as a work piece thickness input by a user. The thickness is the dimension of the work piece A as measured in a direction perpendicular to the surface of the work piece to be cleaned. The controller has a memory function to which there is provided with an adjustment factor. The controller calculates a predetermined target distance between the carriage frame 22 and the conveyor 13 by reducing the work piece thickness input by the user by the adjustment factor. The adjustment factor reduces the work piece thickness input by the user to the predetermined target distance in order to ensure the contact cleaning surface always contacts the work piece as it moves through the apparatus.

The controller energises the electric stepper motor which rotates the cam(s) to move the carriage frame 22 to the predetermined target distance above the conveyor 13. When the work piece A passes between the contact cleaning surface and the conveyor 13, the load applied to the work piece A by the contact cleaning surface is minimised while the optimum cleaning efficiency is obtained. Typically, the predetermined target distance will be equal to the thickness of the work piece A (the work piece thickness input by the user) minus an adjustment factor (e.g. 0.25 mm), to apply the required load. The load is calculated to control the amount of strain in the work piece A during cleaning. The amount of strain in the work piece A is informed by, for example, the IPC/JEDEC-9704A Printed Circuit Assembly Strain Gage Test. The predetermined target distance is also calculated to ensure that all parts of the work piece A are cleaned by the cleaning rollers 21.

Turning now to Figure 4, the work piece A is introduced to the cleaning apparatus 1 via the inlet 11 . The work piece A is placed on the conveyor 13 and is conveyed towards the outlet 12. As the work piece A is conveyed the inlet sensor 6 identifies the presence of the work piece A, and informs the controller; and/or adds a count to the counter; and/or sets a status identifier to indicate that a work piece A is present. Turning now to Figure 5, the controller energises the electric motor to rotate the cams 3. The cams 3 are rotated such that the carriage frame 22 is moved away from the conveyor 13 to the predetermined target distance in order to provide an optimum distance between the conveyor 3 and the cleaning rollers 21 . . The carriage sensor 4 continuously measures the distance between the conveyor 3 and the carriage frame 22 and provides the measurements to the controller which compares the measured distance to the predetermined target distance. The controller then energises the electric motor to rotate the cams 3 to maintain the predetermined target distance.

Referring now to Figure 6, the work piece A is conveyed to between the contact cleaning rollers 21 and the conveyor 13. As the work piece A is conveyed between the contact cleaning rollers 21 and the conveyor 13, the contact cleaning rollers 21 remove particles from the work piece A. The adhesive roll 23 then removes the particles from the contact cleaning rollers 21 . As the cleaning rollers 21 are in contact with the work piece A, the load sensors 5 indirectly measure the load applied to the work piece A by the cleaning rollers 21 by measuring the load applied to the cam surface(s) by the carriage frame 22. If the load measured by the load sensors 5 is outside of a predetermined tolerance, then, depending upon the configuration of the cleaning apparatus 1 , the controller adjusts the height of the carriage frame 22 such that the load applied to the work piece A is within the tolerance; and/or an alert is sent and/or an alarm sounds; and/or the operation of the cleaning apparatus 1 is suspended.

Turning now to Figure 7, the conveyor 13 then conveys the work piece A from between the contact cleaning rollers 21 and the conveyor 13, to the outlet 12, where it is removed from the contact cleaning apparatus 1 . As the work piece A passes the exit sensor 7, the controller is updated to identify that the work piece has exited from between the contact cleaning rollers 21 and the conveyor 13; and/or the counter is updated; and/or the status identifier is updated to indicate that work piece A is not present.

The controller is configurable to rotate the cams 3 to return the carriage frame 22 such that the distance between the contact cleaning rollers 21 and the conveyor 13 is maintained at the predetermined target distance, after the exit sensor 7 has identified that the work piece A has exited from between the contact cleaning rollers 21 and the conveyor 13. The controller is configurable to maintain the carriage frame 22 at the desired height to clean a specific number of work pieces. The number of work pieces can be input to the controller and can be counted by the controller and/or the counter, using information from the inlet sensor 6 and/or the exit sensor 7. The exit sensor 7 can also be used to determine if a work piece should have exited but has not, for example, in the event of a fault. The controller and/or counter obtains readings from the exit sensor 7, and in the event of a fault may, for example, send an alert, raise an alarm and/or suspend the operation of the contact cleaning machine 1 . The controller may also use the readings from the exit sensor 7 to determine when the carriage frame 22 can be returned to a position such that the distance between the contact cleaning carriage 22 and the conveyor 13 is at the predetermined target distance.

A second embodiment of the invention is illustrated in Figure 8. This embodiment is identical in configuration and operation to the embodiment of Figures 1 -7 , except that a carriage sensor 40 is mounted to the carriage frame 22. Accordingly, the carriage sensor 40 moves with the carriage frame 22. This advantageously allows ease of access to the carriage sensor 40 for maintenance, cleaning or replacement carriage frame 22.

To calibrate the position of the carriage frame 22 in either embodiment the controller first determines the absence of a work piece A between the contact cleaning rollers 21 and the conveyor 13. The controller either determines the absence of a work piece A by calculating that the work piece A has exited from between the contact cleaning rollers 21 and the conveyor 13, or by detecting the exiting of a work piece A from between the contact cleaning rollers 21 and the conveyor 13 using the exit sensor 7, if the exit sensor 7 is present.

The controller then rotates the cams 3 such that the distance between the contact cleaning carriage 22 and the conveyor 13 is at the predetermined target distance. This is either achieved by providing a datum on one of the cams 3 or on the cam shaft 31 , or by detecting the point at which the direction of movement changes during rotation of the cams 3. The controller then measures the distance between the carriage frame 22 and the conveyor 13 using the carriage sensor 4, 40.

Alternatively, calibration can be performed by rotating the cams 3 by 360° and recording the distance measured by the carriage sensor 4, 40 throughout the rotation. These measured distances can then be used to overwrite the positions used to control the rotation of the cams 3.

It will be appreciated by the person skilled in the art that variations of the aforementioned embodiments are envisaged. For example, the cam shaft 31 may be rotationally coupled to the carriage frame 22, and the circumferential surfaces of the cams 3 may be in contact with a shelf which is stationary with respect to the conveyor 13. Also, the conveyor 13 may be a roller conveyor instead of a belt conveyor. Furthermore, the contact cleaning rollers 21 may instead be a contact cleaning belt. Also, the contact cleaning apparatus 1 may be a part of a surface mount technology machine.