US20200122290A1

US20200122290A1 - Grinding device

Info

Publication number: US20200122290A1
Application number: US16/604,147
Authority: US
Inventors: Thomas Bettermann
Original assignee: Homag Bohrsysteme GmbH
Current assignee: Homag Bohrsysteme GmbH
Priority date: 2017-04-11
Filing date: 2018-04-10
Publication date: 2020-04-23
Also published as: CN110505939A; EP3609651A1; WO2018189155A1; DE102017206179A1

Abstract

The present invention relates to a grinding device for machining an, in particular plate-shaped workpiece (W). The grinding device comprises an emitter (31) for emitting electromagnetic waves in the direction of the abrasive belt (10) and a detector (32) for detecting electromagnetic waves which are reflected by the abrasive belt (10).

Description

TECHNICAL FIELD

The present invention relates to a sanding device for machining a workpiece, in particular a plate-shaped workpiece, for example a workpiece comprising at least in parts wood, derived timber products, such as wood fibres, etc. In a certain embodiment, the sanding device is a wide-belt sanding machine.

PRIOR ART

The general requirement for sanding devices is that abrasive belts that are used to machine a workpiece with geometrically non-defined cutting edges are monitored or assessed for wear. If such an abrasive belt is worn and this state is not detected or is detected too late, the sanding device will continue to be operated with a faulty or substandard abrasive belt and thus produce rejects.
Normally, the level of wear is determined manually and visually. The abrasive belt is inspected by a worker when the sanding device is switched off and an assessment is made as to whether the abrasive belt should be replaced. This assessment depends greatly on the level of experience of the worker and is therefore prone to error. An assessment based on the workpieces machined is also unfavourable, as once it is recognised that the result of machining is substandard, rejects have already been produced. At this point, the sanding device must be stopped, and the abrasive belt must be replaced, even if the production flow does not simply allow this without disadvantages.
An alternative in industrial use is therefore to replace abrasive belts at an early stage. This means that the abrasive belts are replaced even though it might still have been possible under certain circumstances to continue using them until maintenance is next carried out. As the intervals for replacing an abrasive belt cannot be predicted, or at least cannot be reliably predicted, the precautionary measure described here means that the abrasive belts will be replaced more frequently. The cost associated with this will be deemed to be an acceptable price to pay to maintain quality of production.
Changing an abrasive belt usually has the disadvantage that at least the sanding device, and possibly entire production lines, have to be stopped. This conflicts with the requirement to minimise downtimes as far as possible.
Furthermore, when replacing the abrasive belt, the worker must ensure that the correct abrasive belt is used as a replacement. With an abrasive belt, this is ensured by means of an appropriate marking, for example a number on the surface of the abrasive belt facing away from the grained side. It is also possible to set aside abrasive belts in different colours so that the worker can specifically identify an abrasive belt with a certain grain size and use it correspondingly.
However, due to the dusty working environment in which sanding devices are found, there is always a risk with the known systems that the identifying marking on the abrasive belt is concealed and therefore cannot be correctly identified.

Subject-Matter of the Invention

An object of the present invention is to provide a sanding device to machine a workpiece and a method for identifying the abrasive belt and/or its state, wherein the state of wear of the abrasive belt should be identified according to a preferred requirement.
The subject-matter of claim 1 provides a corresponding sanding device. Further preferred embodiments are described in the dependent claims.
One thought behind the present invention is to use a sensor for electromagnetic radiation, in particular a radar sensor, to identify an abrasive belt and/or determine its level of wear and tear. It has been shown in this respect that the detection result of the sensor, in particular the detected intensity of the radiation reflected on the abrasive belt, provides information about the grain size or the roughness of the abrasive belt, and it is possible to detect, based on further use, if the quality of the abrasive belt has been reduced by wear and tear.
Claim 1 provides a sanding device for machining a workpiece, wherein such a sanding device is preferably used to machine workpieces made from wood or derived timber products. The sanding device comprises a holding fixture for holding an abrasive belt, an emitter for emitting electromagnetic waves in the direction of the abrasive belt and a detector for detecting electromagnetic waves reflected by the abrasive belt.
In this way, it is possible to make an objective assessment of the current quality of the abrasive belt. This can also be done while the sanding device is being operated, thus reducing downtimes and the number of rejects.
In addition, it is possible to determine whether belt cleaning units may not be working correctly. Together with other data from the sanding process, for example monitoring of the actual thickness of the ground workpieces, forecasts for downtimes can be adjusted and updated on an ongoing basis. Identifying repeated wear on one side, for example, can allow conclusions to be drawn about incorrect settings of the machine or unfavourable workpiece geometries.
According to the invention, the sanding device can have a contact roll unit, a sanding unit with a pressure pad, or a transverse sanding aggregate, comprising the holding fixture for holding an abrasive belt. Depending on the design of the sanding unit, the holding fixture can have one, two or more rolls to guide the abrasive belt. Furthermore, the rolls can be aligned so that the abrasive belt grinds a workpiece transversely to or in the direction of the relative movement.
According to a preferred embodiment, it is intended that the emitter and detector are combined in one sensor unit. This enables a robust radar sensor to be provided.
It is also possible that the emitter and detector extend transversely to a direction of movement of the abrasive belt, wherein it is furthermore preferred that the state of the abrasive belt can be monitored across the width of the abrasive belt by the emitter and detector. In particular, the emitter and detector extend transversely to a direction of movement across the entire width of the abrasive belt.
Alternatively, it is intended that the emitter and detector are movable along a guide transversely to the direction of movement of the abrasive belt. The sensor unit, comprising the emitter and detector, can thus be kept relatively compact.
According to a further embodiment, it is intended that the sanding device comprises a conveyor element, in particular a conveyor belt, for moving the workpiece in relation to the abrasive belt. A plate-shaped workpiece can be moved with a conveyor element of this kind, as a result of which it engages with the abrasive belt and is machined.
The holding fixture of the sanding device can comprise a first deflection roll and a second deflection roll, wherein the emitter and the detector are directed at a portion of the abrasive belt located between the deflection rolls, or are pointing in the direction of an area of the abrasive belt where the abrasive belt is resting on one of the deflection rolls. The emitter and detector are positioned so that they are facing in the direction of the abrasive belt.
The holding fixture can also comprise further deflection rolls, for example an upper deflection roll and two deflection rolls adjacent to the conveying element, between which a pressure pad with a sanding pad is placed.
The position with which the emitter and detector are directed towards a portion of the abrasive belt between the deflection rolls has proven advantageous for space reasons, among others. In addition, the abrasive belt presents as a relatively flat surface in this area, thus improving the result of the assessment of the abrasive belt.
Alternatively, it is also possible, as already mentioned, to provide the emitter and detector in the area of the upper deflection roll such that they are facing in the direction of an area of the abrasive belt. Mounting in this area offers the advantage that the abrasive belt is guided relatively smoothly.
In accordance with a further embodiment, the sanding device comprises a display for displaying a detection result of the detector. The display can, for example, be part of a depiction on a screen, or in smartglasses, or can be displayed by a projector. The display can, for example, show the detected intensity of the waves reflected by the abrasive belt.
In one embodiment, a controller is provided that is set up to compare a detection result of the detector, in particular the detected intensity of the waves reflected by the abrasive belt, with the identification data of abrasive belts. This identification data relates, for example, to the grain size of abrasive belts, which are divided into certain categories. It has been shown that different grain sizes can be detected based on different intensities/reflectances with electromagnetic waves, thus allowing conclusions to be drawn about a respective abrasive belt inserted.
In accordance with a further embodiment, the sanding device comprises a warning device for issuing an acoustic or visual signal. This warning device can be triggered if an incorrect or worn abrasive belt is detected. This increases operational reliability and the production of rejects is avoided.
According to a further embodiment, the sanding device also comprises an abrasive belt cleaning unit. This could be a belt blow-off device, for example. According to a modification, it is preferred that operation of the abrasive belt cleaning unit is controlled or monitored based on the detection result of the detector. It is therefore possible to increase the cleaning effect of the abrasive belt cleaning unit for certain abrasive belts and reduce it for other abrasive belts, thereby reducing energy consumption. Furthermore, it is possible to identify whether the abrasive belt cleaning unit is working correctly, such that operational reliability is further increased.
Furthermore, the present invention relates to a method for detecting an abrasive belt comprising the following steps: movement of the abrasive belt in relation to an electromagnetic wave emitter, emission of the electromagnetic waves from the emitter to the abrasive belt, and detection with a detector of the electromagnetic waves that are reflected by the abrasive belt.
This allows an objective assessment of the abrasive belt during operation. As regards further advantages, reference is made to the statements above.
In one embodiment, emission and detection should take place during machining of a workpiece with the abrasive belt or during no-load operation of the abrasive belt. It is therefore not necessary to stop the abrasive belt, which means that downtimes can be reduced.
It is further preferred that the grain size of the abrasive belt may be detected based on the detection result of the detector, in particular the detected intensity of the waves reflected by the abrasive belt. Based on these results, it is therefore possible to draw conclusions about the quality and state of the abrasive belt.
The method can also comprise the following step: display of the detection result of the detector, in particular the detected intensity of the waves reflected by the abrasive belt, on a display. This enables the worker to identify which abrasive belt is being used and/or what the state of the abrasive belt in use is.
According to a further modification, the method comprises the following step: output of a visual or acoustic warning signal if it is identified that the determined grain size of the abrasive belt does not correspond to a specified value, or if it is identified that the detected intensity or the reflectance is less than a first threshold value, or alternatively is more than a second threshold value. This measure allows operational reliability to be further increased.
If a surface of the abrasive belt is relatively “rough” or if it has a coarse grain size, the radiation (preferably radar radiation) is reflected back onto a larger area. If, on the other hand, the surface of the abrasive belt is relatively smooth, in other words if the abrasive belt is relatively heavily worn, for example, a greater portion of the radiation reaches the detector. The detected intensity is therefore higher than for a rougher or more structured surface of the abrasive belt.
Based on the intensity of the radiation arriving at the detector, conclusions can thus be drawn about the “roughness”, and therefore the state, of the surface of the abrasive belt.
In addition, it is possible to identify further operating data of the abrasive belt, such as the speed of movement of the abrasive belt or the slip of the abrasive belt during operation.
This data can be processed in the controller of the sanding device and be used to monitor operation of the sanding device.
In addition to the advantages already mentioned, the sanding device according to the invention and the method according to the invention therefore also offer the possibility of improved quality control. Furthermore, additional data about the machining process can be obtained with a relatively inexpensive measure, and said data can generally be factored into possible maintenance periods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a sanding device for which partial wear of an abrasive belt is detected.

FIG. 2 is a schematic side view of the sanding device shown in FIG. 1.

FIG. 3 shows a sanding device for which the type of a certain abrasive belt is identified.

FIG. 4 is a schematic representation of a sanding device for which another type of abrasive belt is identified.

FIG. 5 shows a second embodiment of the present invention.

FIG. 6 shows a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below with reference to the accompanying figures in order to illustrate the present invention by way of examples. Further modifications of certain individual features cited in this context can each be combined to create additional embodiments.
With reference to FIGS. 1 and 2, a sanding device according to an embodiment of the present invention will be described below. Such a sanding machine can be used to produce or machine furniture parts or elements for the structural elements industry.
By way of an example of a conveyor element, the sanding device comprises a rotating conveyor belt 20 that moves a plate-shaped workpiece W in a conveying direction F. Such a workpiece W is made from wood or derived timber products, for example.
A sanding unit 1 is provided vertically above the conveyor belt 20 and features an upper roll 15 and a lower roll 16 around which an abrasive belt 10 rotates. In the present exemplary embodiment, the sanding unit 1 is what is known as a contact roll unit.
The abrasive belt 10 engages with the workpiece W moved with the conveyor belt 20 and removes portions of the surface of the workpiece W by machining. Alternatively, a polishing process can be performed.
The sanding device shown in the figures is only shown schematically. This means that sanding devices are also included that comprise one upper roll and two lower rolls. A transverse sanding machine can also be cited purely as an example of an alternative to a wide-belt sanding machine.
In the present exemplary embodiment, a sensor unit 30 positioned between the upper and lower roll comprises an emitter 31 for emitting electromagnetic waves and a detector 32 for detecting electromagnetic waves reflected by the abrasive belt 10. The sensor unit 30 can also be referred to as a radar sensor. For illustration purposes, the emitter 31 and detector 32 are shown as separate units in the schematic drawings. However, the emitter 31 and detector 32 can also be combined into a single unit.
It is apparent that the position of the sensor unit 30 can be varied. For example, the sensor unit 30 can be placed above the upper roll 15. It is also possible to place the sensor unit 30 to the side of the upper roll 15.
According to a first possible application it is intended that the sensor unit 30 detects whether certain areas of the abrasive belt 10 are worn.
In the example shown in FIG. 1, the abrasive belt 10 comprises a less worn portion 10 a and a heavily worn portion 10 b. The level of wear and tear can be shown in a chart (display) 40, for example, that the worker can read as part of a screen display. Based on the chart 40, the worker can identify whether certain areas of the abrasive belt 10 are already heavily worn, enabling the worker to decide whether to have workpieces W machined by the portion 10 b of the abrasive belt 10 that is not yet worn. This is achieved by varying the position of insertion. Alternatively, the worker can identify that a replacement of the abrasive belt is required.
It is conceivable in this context that a suggestion will be made to the worker based on the detection result. For example, a display may be issued on a screen of the sanding device indicating that a replacement of an abrasive belt is expected to be required after a certain number of machining operations. This would therefore allow the sanding device to be operated predictively, as the worker is already able to prepare for the forthcoming replacement of the abrasive belt, be this by ordering a new abrasive belt, for example.
As part of the embodiment described, it is possible that detection by the sensor unit 30 takes place during operation, in other words while still machining a workpiece W, or that detection by the sensor unit 30 is performed during no-load operation of the sanding device.
According to a further possible application (FIGS. 1 and 2), the sensor unit 30 is used to recognise a certain abrasive belt 10. An abrasive belt is normally “recognised” by a worker, as it has a certain marking and/or colour. However, the disadvantage of a marking is that the marking may be difficult to read automatically. A further disadvantage is that the marking is only placed in a certain position of the abrasive belt and this position of the marking would in the first instance at least have to be identified by the worker. If an abrasive belt that is not suitable for the planned machining is inserted into the sanding device, rejects will initially be produced until the worker recognises his or her error.
With the sensor unit 30, it is now possible to determine different grain sizes based on the detected intensity of the electromagnetic waves reflected on the abrasive belt.
If a surface of the abrasive belt is relatively “rough” or if it has a coarse or largely unchanged grain size, the radiation (preferably radar radiation) is reflected back onto a larger area. The detected intensity is therefore lower. If, on the other hand, the surface of the abrasive belt is relatively smooth; in other words, if the abrasive belt is relatively heavily worn, for example, a high portion of the radiation reaches the detector. The detected intensity is therefore higher than for an abrasive belt with a rough surface.
Based on the intensity of the radiation arriving at the detector, conclusions can therefore be drawn about the “roughness”, and therefore the state, of the surface of the abrasive belt.
It is therefore possible that the controller of the sanding device is provided with information regarding the abrasive belt actually inserted. This information can be shown on either a screen or similar, for example in chart 40, in order to provide the worker with information about the abrasive belt inserted. If an abrasive belt with the wrong grain size is recognised for the next pass, a warning (visual or acoustic) can also be output.
Alternatively, it is possible to forward the information to the machine control system in order to make settings on the sanding device that correspond to the abrasive belt currently inserted.
FIG. 3 shows a sanding device according to the first embodiment, wherein the type of the abrasive belt 10 is detected, as a relatively low intensity is shown in the display 40. In FIG. 4, a different abrasive belt 10 has been inserted, meaning that a different intensity across the width of the abrasive belt is shown in the display 40.
A qualitative assessment of the abrasive belt can be performed based on a comparison of the edge areas with a centre area of the abrasive belt, for example, in particular if it can be assumed based on the type of use that the original grain size is present in the edge area while wear and tear has occurred in the centre area.
A second embodiment of the present invention is shown in FIG. 5. Corresponding or identical elements that have already been described in the context of the first embodiment are provided with similar or identical reference numbers.
In the context of the second embodiment, a sanding unit 1′ is provided instead of sanding unit 1. Instead of a lower roll 16, the sanding unit 1′ has a calibration roll 16 a, a deflection roll 16 b and a pressure pad 16 c. The pressure pad 16 c is used to press certain portions of the abrasive belt 10 against a workpiece (not shown here) resting on the conveyor belt 20 and moved with the conveyor belt 20. Alternatively, it is possible to perform sanding in the area of the calibration roll by adjusting the calibration roll 16 a accordingly in the direction of the conveyor belt.
The sanding unit 1′ has a sensor unit 30′. The sensor unit 30′ comprises a rail 33 along which an emitter 31′ and a detector 32′ can be moved, wherein the emitter 31′ and the detector 32′ are combined into a single unit in the present embodiment.
A possible display result is shown in the display 40′ purely by way of example. Once the movable unit comprising the emitter 31′ and the detector 32′ in the present exemplary embodiment has already travelled a certain section along the abrasive belt 10′ (from left to right in FIG. 5), the area already scanned can be read on the display 40′.
A third embodiment of the present invention is shown in FIG. 6. Similarly to the first and second embodiments, the third embodiment has a conveyor belt 20 for moving a workpiece W. In addition, the third embodiment has a sanding unit 1 according to the first embodiment, a sanding unit 1′ according to the second embodiment and also a transverse belt sanding unit 1″.
In the present exemplary embodiment, the transverse belt sanding unit 1″ has two abrasive belts 10″ that are guided by means of appropriate deflection rolls. Furthermore, a sensor unit 30″ and corresponding display 40″ are provided for each of the abrasive belts 10″.
The third embodiment is intended to illustrate that various sanding units can be combined and that a display can be used for the sanding unit in question in order to perform the previously discussed assessments of the respective abrasive belts.
In this regard, it is apparent that the order of the sanding units can be varied in order to create further embodiments. Embodiments having only two of the aforementioned sanding units are also conceivable.
Furthermore, it is apparent that the various displays can be combined into one view, for example into a display on a monitor that is used to monitor the sanding machine.
A user can read off values for the various abrasive belts from the displays 40, 40′, 40″ depicted in FIG. 6. In particular, the fact that the abrasive belt of the sanding unit 1 is partially worn and one of the abrasive belts of the sanding unit 1″ is completely worn is displayed. According to the display 40′, the abrasive belt 10′ of the sanding unit 1′ is in a good state, as a relatively high intensity is displayed according to the display 40′.
The displays 40, 40′, 40″ can be shown on a screen either separately or in a shared view.

Claims

1. A sanding device for machining a workpiece, comprising:

a holding fixture for holding an abrasive belt,

an emitter for emitting electromagnetic waves in the direction of the abrasive belt, and

a detector for detecting electromagnetic waves that are reflected by the abrasive belt.

2. The sanding device according to claim 1, characterised in that the emitter and the detector extend transversely to a direction of movement of the abrasive belt across the entire width of an abrasive belt, or the emitter and the detector can be moved along a guide transversely to the direction of movement of the abrasive belt.

3. The sanding device according to claim 1, characterised in that the sanding device comprises a conveyor element, in particular a conveyor belt, for moving the workpiece in relation to the abrasive belt.

4. The sanding device according to claim 1, characterised in that the holding fixture comprises a first deflection roll and a second deflection roll, wherein a pressure pad for pushing the abrasive belt against a workpiece is provided.

5. The sanding device according to claim 4, wherein the emitter and detector are directed at a portion of the abrasive belt located between the deflection rolls or are pointing in the direction of an area of the abrasive belt where the abrasive belt is resting on one of the deflection rolls.

6. The sanding device according to claim 1, characterised in that the sanding device has a display for displaying the detected intensity of the reflected waves by the detector.

7. The sanding device according to claim 6, characterised in that the sanding device comprises a controller that is set up to compare a the detected intensity of the reflected waves, with identification data of the abrasive belts.

8. The sanding device according to claim 1, characterised in that the sanding device comprises a warning device for issuing an acoustic or visual signal.

9. The sanding device according to claim 7, characterised in that the sanding device furthermore comprises an abrasive belt cleaning unit, wherein it is preferable that operation of the abrasive belt cleaning unit is controlled and/or monitored based on the detection result of the detector.

10. The sanding device according to claim 1, characterised in that a radar sensor is used as an emitter and detector.

11. A method for examining an abrasive belt, comprising the following steps:

emission of electromagnetic waves to the abrasive belt, and detection of electromagnetic waves reflected by the abrasive belt.

12. The method according to claim 11, characterised in that the emission and detection takes place during machining of a workpiece with the abrasive belt or during no-load operation of the abrasive belt.

13. The method according to claim 11, characterised in that the grain size and/or level of wear of the abrasive belt is/are identified based on the detection result of the detected intensity of the reflected waves.

14. The method according to claim 13, further comprising the following step: display of the detection result of the detected intensity of the reflected waves, by means of a display.

15. The method according to claim 13, further comprising the following step: output of a visual or acoustic warning signal when it is identified that the determined grain size of the abrasive belt does not correspond to a specified value, or when it is identified that the detected intensity of the detected electromagnetic waves is below a first threshold value or above a second threshold value.